General Motors unveiled updates to its 2027 heavy-duty truck lineup, the Chevrolet Silverado HD and GMC Sierra HD, including a new Duramax 8.3L Turbo-Diesel V8 engine that delivers increased horsepower and torque, plus electric power steering and electronic brake boost.

GM reports that more than 60% of heavy-duty customers opt for a diesel engine when purchasing a truck, and its brands already account for the majority of diesel-powered share in the segment.

Speaking at the Pontiac Engineering Center, where GM engines are developed and validated long before they ever hit the plant floor, Ken Morris, senior vice president of product integration, provided more details of how GM developed the new L6P, and more.

“So, for 2027, our philosophy was simple: we didn't just build a bigger engine; we built a confidence-inspiring truck around the bigger engine. To pull that off, vehicle integration has to be a primary focus. It's how we ensure that the powertrain, the braking, the steering, and the chassis don't just exist on the same frame, but work together as one seamlessly coordinated system. We took the foundation built right here in Pontiac and pushed it to the extreme in Milford, perfectly matching the engine's raw power to the truck's driving dynamics.”

He said the clean-sheet diesel engine introduced for 2027 is the first all-new high-performance diesel GM has designed, developed, and manufactured completely in-house.

“It's the most capable, durable, and relentless diesel powerhouse we have ever built, delivering best-in-class horsepower and best-in-class torque,” Morris added.

“We're building on GM's full-size truck leadership by enhancing and reinventing the elements of the truck that customers rely on most. Starting with power,” said Jaclyn McQuaid, senior vice president, vehicle products. “We know that HD drivers have intense towing demands. Over 70% of HD owners tow every month and drive on average 4,300 towing miles annually. So, we're bringing two engines to the table that are more than up to the task.”

Those new engines for the 2027 HD lineup are the:

• Duramax 8.3L Turbo-Diesel V8 (L6P)
• 6.6L Gas V8

Duramax 8.3L Turbo-Diesel

“You've heard me refer to it as the L6P, but most of our development team knows it by a different internal name: Mongoose,” McQuaid said. “Now, on the diesel, properly equipped models can tow up to 38,000 pounds. That is the equivalent weight of a fully loaded fighter jet.”

GM has helped transform the HD pickup segment, said Glenn Babiak, vehicle chief engineer for the 2027 heavy-duty program, and plans to keep doing so in the future. He touted the new engine as class-leading with 555 horsepower and 1,230 lb.-ft. of torque, while emphasizing it was a clean-sheet design.

Rob Moran, assistant chief engineer for the heavy-duty diesel engines at GM, explained that when the company launched the Duramax in 2001, it featured 300 horsepower and 520 lb.-ft. of torque. The current generation of the L5P delivers 470 horsepower and 975 lb.-ft. of torque, which will now be significantly surpassed by the L6P.

“The newest Duramax turbo diesel V8 is more than just an upgraded engine. It's a clean-sheet heavy-duty diesel architecture that we've developed specifically around the demands of heavy-duty truck customers. This approach allowed the engineers to rethink all the major systems together, from crankcase, rotating assembly, air management, lubrication, cooling controls, and aftertreatment,” Moran explained. “And the result that you see here is a foundation designed to support increased performance potential, increased towing capability, efficiency, refinement, and lower emissions.”

Moving forward, starting with the 2027 GM HD pickups, the L6P is the only diesel powertrain option that will be offered.

Key benefits of the new diesel engine, according to GM, include:

• All-new, GM-developed HD diesel architecture, designed specifically around heavy-duty pickup customers, with a compacted graphite iron cylinder block, full-forged crankshaft, connecting rods, and steel pistons forming the foundation for strength and durability.

• More confident power and towing, with best-in-class diesel horsepower and torque, supported by a broad torque curve, high-flow fuel injection, and vehicle integration focused on launching heavy trailers, climbing grades, and maintaining control under load.

• Advanced cooling and charging systems built for towing, including a compact dual-stage air-to-water charge cooling system, high-efficiency variable-geometry turbocharger, and upgraded engine-cooling strategy to help deliver consistent performance when the truck is working hard.

• Improved refinement and drivability, with the new engine architecture, integrated intake design, advanced combustion system and crankshaft isolation hardware helping reduce noise and vibration while supporting a more confident HD driving experience.

• Integrated diesel system engineered as a complete package, pairing the engine with the Allison 10-speed transmission, upgraded exhaust braking capability and a new aftertreatment layout designed to support heavy-duty performance, regeneration functionality and customer confidence over long-distance towing.

“This new diesel engine is the culmination of decades of GM diesel development and integration,” said Norman Peralta, executive chief engineer, global engine and battery systems. “From the clean-sheet architecture and combustion system to the cooling, aftertreatment and transmission calibration, this is a powertrain built with heavy-duty purpose and pride.”

GM will build the new engine at its expanded DMAX facility in Brookville, Ohio, a 1.4-million-square-foot plant that brings machining and assembly under one roof. GM previously invested $920 million to expand DMAX to handle this high-volume engine program.

GM’s New 6.6L Gas V8

The 6.6L gas V8, assembled at GM’s Tonawanda Engine Plant in New York, also gains horsepower and torque, with improved low-end pull and updated emissions hardware supported by a new turbo-Jet intake manifold, revised lubrication system, engine-mounted oil cooler, and digital oil-level display.

Like the diesel, the updated 6.6L gas V8 is paired with the Allison 10-speed 10L1000 transmission and advanced shift logic to help keep each engine in its optimal range for smoother acceleration, stronger grade performance, and more confident control with heavy trailers.

Electric Power Steering: Precision Control for HD Pickups

For 2027, GM’s HD pickups move to an all-new rack-and-pinion electric power steering system, a segment-first for heavy-duty trucks, replacing the previous hydraulic-assisted steering system with an all-new electric power steering architecture designed specifically for heavy-duty truck demands.

“We moved away from the recirculating ball steering system to an advanced rack-and-pinion-style fail-safe EPS system.  The system delivers approximately 30% higher output than the current system, and it is fully self-redundant,” Babiak explained. “It has dual-power, dual-cam, redundant ECUs and redundant torque and angle sensors, so it is very much designed and developed for heavy usage. Since it is EPS, it eliminates the hydraulic pump, reservoir, coolers, and fluid lines, and by doing that, it obviously removes the traditional hydraulic steering noises and potential weak points.”

The electric power steering system, according to GM, helps deliver:

• Higher steering output built for serious work, with approximately 30% more power than the current HD hydraulic steering gear to support heavy front-axle loads, low-speed maneuvering, towing, and demanding work-truck use.
• More precise, consistent steering in demanding conditions, with expanded drive-mode tuning, improved on-center feel, and reduced kickback to help drivers feel more in command on highways, job sites, rough roads, and trails.
• A cleaner, quieter, and lower-maintenance system, eliminating hydraulic pumps, hoses, fluid, and related hardware to reduce traditional steering noise, lower system complexity, and improve the ownership experience for customers who depend on their trucks every day.

HD-grade durability and protection, with built-in system redundancy plus corrosion- and impact-resistant hardware designed for harsh heavy-duty truck environments, including rough terrain, road debris, and severe-duty use.

Together, the new EPS system provides GM’s HD trucks a modern steering foundation—one that is stronger, quieter, and more precisely tuned for the way customers use their trucks. From tight low-speed maneuvers and heavy towing to rough roads and off-road terrain, the system is designed to help drivers feel more connected, more in control and more confident behind the wheel.

Stopping Power & Brake Intelligence

Featuring a segment-first electronic brake-boost system in a heavy-duty pickup, GM is introducing modern brake technology to the HD segment while still delivering the strength customers expect.

“For 2027, the trucks also have eBoost. It is the first for the segment to have eBoost, and we also upgraded the foundation brakes. An eBoost brake system allows you to custom tune that brake pedal feel for a more modern, refined pedal experience,” Babiak said. “It also is a redundant system. Two modes go into that system, so if one fails, you have the backup for when you need it.”

“So, let's talk about the foundation brakes,” he continued. “We moved to a four-piston fixed front caliper. We upgraded front and rear rotors, providing more braking force and cooling. We enhanced the thermal performance of the system, 20% in front, 40% rear. Improved fade resistance and trailer confidence. Enhanced diagnostics can also indicate brake fade and leaks earlier, and closer integration with active safety systems supporting a more refined response.”

Benefits of the new electronic brake-boost system, according to GM, include:

• First-ever electronic braking for an HD pickup, designed for heavy-duty capability and control.
• Stronger, more consistent stopping performance, with larger 14.6-inch front rotors, new four-piston fixed front calipers, and upgraded rear hardware that help improve thermal capacity, stiffness, and braking confidence with big trailers.
• More linear, predictable pedal feel, with reduced pedal travel, a new pedal position, and a refined pedal feel help make braking feel shorter, smoother, and more confidence-inspiring in everyday driving, towing, and hauling.
• Smarter braking integration, supporting advanced driver-assistance features like Adaptive Cruise Control and Automatic Emergency Braking, while enhanced diagnostics help detect conditions such as brake fade or leaks sooner.
• Cleaner, lighter, and more refined system architecture, eliminating the shared hydraulic source for steering and braking to reduce complexity, remove weight, improve low-speed steering feel, and support more consistent brake-control tuning on pavement and off-road.

Together, the new brake system gives GM’s HD trucks what the company called “a modern, confidence-inspiring braking foundation—one that reacts more precisely and works seamlessly with the truck’s steering, chassis and driver-assistance technologies.”

Drive Modes for a Variety of HD Scenarios

The 2027 HD lineup expands GM’s coordinated drive-mode strategy so powertrain, steering, braking and chassis systems respond together to towing, hauling, highway driving and off-road demands.

Available drive modes include:

• Normal – Everyday calibration for commuting and unloaded driving.
• Tow/Haul – Tailors engine mapping, shifting, exhaust brake, grade-braking, EPS assist, and electronic brake-boost tuning to support heavy towing and hauling with more stability and control.
• Off-Road – Adjusts ABS, traction control, and stability control to allow more wheel slip and side slip on loose surfaces, supported by EPS and eBoost tuning that cut harsh feedback.
• New Terrain Mode (ZR2 / AT4X) – A first for GM’s HD trucks, enabling one-pedal off-road driving in 4HI and 4LO; lifting off the accelerator automatically applies braking for precise control on steep grades and technical obstacles.

Trailering Capability & Technology

2027 HD models are engineered to offer serious towing, with capability of up to 46,500 pounds GCWR and up to 38,000 pounds max trailering on select configurations.

Core updates related to towing include:

• Higher max available trailering capability, with properly equipped models offering up to 38,000 pounds max trailering, and every diesel dually model is capable of towing up to an available 30,000 lbs. or more.
• More confidence with heavy loads, with revised chassis, suspension, steering and braking systems tuned together to help the truck feel stable, predictable and controlled when towing at or near maximum ratings.
• Powertrains built to pull, pairing the available all-new Duramax 8.3L Turbo-Diesel V8 and enhanced 6.6L gas V8 engines with the Allison 10-speed transmission and updated shift strategies to help launch heavy trailers, climb grades and manage downhill control.
• Available visibility technology for easier towing, including up to 14 available camera views such as Transparent Trailer View, Bed View and Surround Vision to help with hitching, lane changes, reversing and trailer monitoring.
• Integrated trailering support from setup to the road, with the available in-vehicle trailering app, available Trailer Side Blind Zone Alert, and available trailer tire pressure and temperature monitoring helping drivers prepare, connect, and stay aware while towing.

The 2027 HD lineup is engineered to make heavy towing feel easier, smarter, and more secure—combining added capability with integrated technologies that help drivers hitch, maneuver, climb, descend, and tow big loads with greater confidence.

Available at U.S. Dealers in Late 2026

The 2027 Chevrolet Silverado HD and GMC Sierra HD are expected to arrive at U.S. dealers beginning late 2026. MSRP and additional product information will be announced in future updates.