Flint Assembly in Michigan is currently wrapping up Silverado HD and Sierra HD turbo diesel truck production for model year 2026. Starting November 16, the 2027 models with the new Mongoose engine will be rolling off the assembly line.
This information comes from GM Trucks, which underlines that Flint builds the 2500 and 3500 versions of the Silverado HD and Sierra HD, including duallies. Over at General Motors, the Detroit-based automaker says that both 2027 models would launch in the latter part of 2026.
General Motors further assembles HD trucks at its Oshawa facility in Canada. The 8.3-liter Duramax, meanwhile, hails from the DMAX facility in Ohio. Internally referred to as L6P as opposed to L5P for the diesel engine it replaces, the newcomer develops a best-in-segment 555 horsepower. Peak torque is estimated at 1,230 pound-feet (1,668 Newton-meters).
That makes the L6P a lot punchier than its forerunner, which is only natural given the difference in displacement. Opting for the 8.3-liter unit results in another 85 horsepower and 255 pound-feet (346 Newton-meters), figures that unlock slightly higher maximum towing figures.
GM says the L6P is a clean-sheet design. Compared to the standard naturally aspirated small-block V8, which boasts 6.6 liters, the diesel option costs $11,400 for model year 2027 as opposed to $9,900 for its predecessor. The outgoing L5P still has a compelling argument for many customers, giving service technicians a very familiar platform to work on.
Photo: GM
New powertrains, especially those developed specifically for towing this much, are way more susceptible to minor and major issues. We also have to remember that Chevy and GMC dealers will be much obliged to get rid of 2026 models by offering end-of-production incentives.
Paired with a 10-speed automatic that carries Allison branding even though it’s not a true Allison tranny, said engine is compatible with B20 fuel and uses a compacted graphite iron block. Forged conrods, a forged crank, and forged pistons also need mentioning, along with a variable-geometry turbo, dual stage air-to-water charge cooling, piston-cooling oil jets, a variable-displacement oil pump, and new exhaust after-treatment goodies.
As far as the Silverado HD is concerned, the Chevrolet division lists a maximum available towing capacity of 38,000 pounds (17,237 kilograms). Maximum payload comes in at 6,170 pounds (2,799 kilograms). Downgrading to the 6.6-liter gasoline V8 results in maximum figures of 19,000 and 6,990 pounds, respectively, meaning 8,618 and 3,171 kilograms in metric speak.
L8S is the regular production option code of the gasser, which replaces the L8T in the heavy-duty truck range. Assembled in Tonawanda, New York, this lump generates a very respectable 412 horsepower and 472 pound-feet (640 Newton-meters) of twist on regular unleaded.
Major differences over the L8T include the redesigned intake manifold, which boosts airflow efficiency, an upgraded cooling system that includes a redesigned water pump, new internal oil passages, a different oil pan, and a digital oil level display in the instrument cluster instead of a dipstick. Both mills are joined by rack-and-pinion electric power steering.
For model year 2027, the HD trucks also get an electronic brake-boost system. The final highlights come in the form of updated Tow/Haul and Off-Road modes.