General Motors is expanding its lineup of heavy-duty pickups and vans fueled by compressed natural gas and propane autogas for the 2017 and 2018 model years, which will bring its alternative fuel lineup to more than 25 vehicles.

Chevrolet and GMC will partner with Power Solutions International, Inc. (PSI) to equip the vehicles with the alternative-fuel powertrains. GM will use its ship-through network to deliver the vehicles to dealers where a fleet representative could pick it up. Fleets can begin ordering vehicles in the first quarter of 2017.

GM will offer the alternative powertrains for Chevrolet vehicles including the Express Cargo (2500, 3500, and 4500), Express Passenger (2500 and 3500), Silverado HD, and Low Cab Forward (3500 and 4500). GMC vehicles include the Savana Cargo (2500, 3500, and 4500), Savana Passenger (2500 and 3500), and Sierra HD.

In a related announcement, GM selected the Wood Dale, Ill.-based PSI as its preferred upfitter for CNG and LPG (liquefied petroleum gas) trucks.

The vehicles will be powered by GM's 6.0L V-8 engine, which will arrive at PSI with hardened valves and valve seats. PSI will install the alternative fuel system and other hardware. The vehicle modifier will then ship the finished vehicle to Chevrolet or GMC dealers.

Following the modification, the five-year or 60,000-mile limited powertrain warranty remains in tact.

The expanded lineup brings GM Fleet's portfolio of alternative fuel, hybrid, and battery-electric vehicles to more than a dozen trucks, cars and crossovers. Other recent additions include the Chevrolet Bolt EV, a Duramax 2.8-L B20-capable Duramax diesel for the Chevrolet Express and GMC Savana vans and available 6.6L B20-capable Duramax diesel engines for the Chevrolet Silverado HD and GMC Sierra HD.