The 2020 model-year marks the first full model-year the 3.0L Duramax diesel engine and 10-speed transmission are available as an option.
 - Photo: Eric Gandarilla

The 2020 model-year marks the first full model-year the 3.0L Duramax diesel engine and 10-speed transmission are available as an option.

Photo: Eric Gandarilla

Media had the opportunity to test-drive the 2020 GMC Sierra diesel models in Wyoming.

It’s hard not to enjoy driving the Sierra HD: with a max tow rating of 35,500 pounds, it handled everything thrown at it on a recent media drive. A suite of technology offerings made the towing experience mostly stress-free, regardless of experience.

Also, a few days behind the wheel of the 2020 GMC Sierra 1500 diesel painted a picture of a fuel-efficient, comfortable, and capable towing machine.  

Heavy-Duty Towing Capability

Towing a camper with the Sierra HD at cruising speeds didn’t feel like you were hauling nearly 13,000 pounds. With the Sierra HD diesel’s max towing capability of 35,500 pounds (52% more than the previous generation) that shouldn’t have been too surprising.

Even with that much weight attached, the Sierra HD confidently handled going uphill, the truck never really felt like it was exerting itself to handle the task. An exhaust brake button allowed us to choose whether the truck would help with braking going downhill. 

With the exhaust brake on, it felt like the truck was ensuring a proper descent speed on its own, and I rarely had to apply the brakes manually. With the exhaust brake off, going downhill was a much more involved process.

Apart from the truck assisting the driver while going downhill, the Sierra HD also includes a park grade hold assist, which enhances its hill hold assist by using all four tires to keep the truck in place. GMC stated this reduces strain on the transmission and prevents sliding for a smoother experience when shifting in and out of park.

2020 GMC Sierra 1500 
Diesel Specs:

  • Engine: 3.0L Duramax I-6 turbodiesel (277 hp, 460 lb.-ft.)
  • Transmission: 10-speed automatic transmission
  • Payload: 7,442 pounds
  • Towing: 9,100 pounds

Off the line, the truck hardly struggled to get to speed. You felt the weight behind you, but it didn’t take long for the truck to reach speed. From there, it was smooth sailing.

This off-the-line experience is partly thanks to the fact that General Motors has engineered the HD’s 6.6L Duramax turbo-diesel engine and Allison 10-speed transmission to provide all of its 910 lb.-ft. of torque in first gear.  

With an 18,000-pound trailer attached, GMC stated it would take its Sierra HD 19.9 seconds to go from 0 to 60 mph, 18.2 seconds to go from 25 to 60 mph, and 11.8 seconds to go from 40 to 60 mph on a flat path.

On a separate day, we drove the Sierra HD with 2,000 pounds of logs in the box. At the end of the drive, I almost forgot they were there.

One of the biggest standouts through the drive was just how smooth the ride was. According to GMC, the smooth ride is a result of engineering the Sierra HD with an independent front suspension that provides better ride shake and ride comfort while trailering.

GMC is offering factory-installed power take-off (PTO) Allison 10-speed transmission-equipped Sierra HDs.
 
 - Photo: Eric Gandarilla

GMC is offering factory-installed power take-off (PTO) Allison 10-speed transmission-equipped Sierra HDs.
 

Photo: Eric Gandarilla

Heavy-Duty Safety

GM’s 15-view camera system — which is also found in the 2020 GMC Sierra 1500 and Chevrolet Silverado — was also a big help during the drive experience. Transparent trailering continues to be a joy to use, as it provides a clear picture of what’s behind you even when towing a large trailer.

2020 GMC Sierra 2500/3500 Diesel Specs: 

  • Engine: 6.6L Duramax turbo diesel (445 hp, 910 lb.-ft.)
  • Transmission: Allison 10-speed transmission
  • Payload: TBD
  • Towing: 35,500 pounds

All the other camera views are useful and have their place, like providing unobstructed views of your left and right side when signaling left or right, but it never gets old to turn the hulking trailer behind you invisible.

Additionally, tech available on the Sierra 2500/3500 includes a segment-first rear camera mirror. A multicolor head-up display — which projects customizable data such as speed, navigation, etc., on the car windshield — is also available. 

Also, it’s hard not to notice the truck’s six-function tailgate, which offers various solutions and, in my experience, made getting to certain parts of the box much more manageable. 

For interested fleets, GMC is offering factory-installed power take-off (PTO) Allison 10-speed transmission-equipped Sierra HDs.

The Mid-Size Diesel Option

Although the 3.0L Duramax diesel engine and accompanying 10-speed transmission were available as an option for the Sierra 1500 late into its 2019-MY, the 2020 model-year marks the first full model-year the engine and transmission is available on the Sierra 1500.  

To get a sense of how capable the diesel Sierra is, GMC attached an 8,000-pound trailer to the back of the truck and had us drive through a mountainous route full of inclines and declines of various grades.

Even with minimal towing experience, I felt fully in control of the truck as I drove through the route. Going uphill, the truck’s 277 hp and 460 lb.-ft. of torque never really felt like it struggled with the heavy load. This is likely due to GM’s focus on torque over horsepower on this engine.

GM fleet customers have told the company that they don’t need high horsepower, they need something fuel-efficient that can move quickly off the line with a heavy load behind it. To meet these requests, GM focused on low-end torque. And, on the topic of fuel economy, the 2020 Sierra 1500 diesel is the most fuel-efficient Sierra ever at 30 mpg highway.

An automatic exhaust brake would kick in to limit how fast the truck went downhill. This automatic exhaust brake feature alleviated a lot of the worry that I had about some of the steeper declines. I didn’t have to worry about braking as much going downhill, as the truck did most of the job for me.  

The 15-camera views available as part of GMC’s Enhanced ProGrade Trailering (the same system that was first available in the 2019 Chevrolet Silverado) further helped calm the worries I had with trailering.

The transparent trailer camera view was the standout for me, as it provided a clear view of the vehicle behind me at times when the side mirrors and rear-view mirror couldn’t.

A segment-first available on the 2020 GMC Sierra is a multicolor head-up display that projects customizable data onto the windshield. 

Since I was wholly reliant on the navigation system to get me around our route, I found the combination of projecting my navigation system onto the head-up display and displaying the transparent trailer view on the center screen an ideal combo.

Two other camera views that helped while towing were the left- and right-side-of-the-vehicle views that automatically came up when signaling left or right. 

One last feature that stood out during my time with the Sierra 1500 was an available CarbonPro box. According to GMC, this carbon fiber pickup box is the industry’s first and provides substantial dent, scratch, and corrosion resistance. My experience with this box was watching people beat it violently with an aluminum bat. The box suffered no damage, but the bat ended with a nasty bend.

The 2020 Sierra 1500 diesel costs the same amount as the 6.2L V8 model, $2,495 over the 5.3L V8, and $3,890 over the 2.7L turbo I-4. The diesel engine is available on all trims except the base Sierra trim. 

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