How GM’s New 8.3L Duramax Stacks Up Against Ford and Ram

GM is taking aim at Ford and Ram with a new 8.3-liter Duramax that makes 555 horsepower and 1,230 lb-ft of torque. The diesel coming to the 2027 Chevrolet Silverado HD and GMC Sierra HD beats both rivals’ published high-output engine ratings, but how much of an advantage does that give truck buyers?

Against Ford’s high-output Power Stroke, GM gains 55 horsepower and 30 lb-ft. Against Ram’s high-output Cummins, the gap grows to 125 horsepower and 155 lb-ft. Here is how the three engines compare on paper, and what those numbers still cannot tell us.

Duramax vs. Power Stroke vs. Cummins: The numbers

Ford’s high-output 6.7-liter Power Stroke V8 is the closest rival, with 500 horsepower and 1,200 lb-ft. GM’s advantage works out to 11% more horsepower but just 2.5% more torque. That is a clear paper win, though the relatively small torque gap is worth keeping in perspective. These Ford figures apply specifically to the high-output option.

Ram’s high-output 6.7-liter Cummins takes a different approach with an inline-six and an eight-speed automatic, compared with the V8s and 10-speed automatics in the GM and Ford trucks. At 430 horsepower and 1,075 lb-ft, the Cummins trails GM by about 29% in horsepower and 14% in torque. Cylinder layout and gear count alone do not establish which truck will pull a particular trailer better.

What GM changed to get ahead

GM’s outgoing 6.6-liter L5P Duramax makes 470 horsepower and 975 lb-ft. The new engine adds 85 horsepower and 255 lb-ft, roughly 18% and 26%, respectively. Peak torque arrives at 1,400 rpm, giving the new diesel its maximum rated twist low in the rev range.

The larger displacement comes with a new architecture: a compacted graphite iron block, a forged crankshaft and connecting rods, steel pistons and water-to-air charge cooling. GM pairs the engine with an Allison 10-speed automatic and upgraded exhaust braking. Those changes explain the development effort behind the output increase, but they do not substitute for a loaded comparison test.

There are ownership details beyond the output contest. GM’s engineer told Pickup Truck + SUV Talk the diesel uses gear-driven pumps and retains a physical oil dipstick alongside an oil-level sensor. The aftertreatment system has two diesel exhaust fluid injectors and a manual regeneration function at idle. Our 8.3-liter Duramax engineering report goes deeper into the new design.

More torque does not automatically mean more towing

A trailer is pulled by a complete truck, not an engine rating. Payload, axle ratings, combined weight limits, hitch type and the weight of passengers and cargo can constrain what an individual truck can tow. Gear ratios, cooling and braking also matter when comparing how confidently it handles a load.

Properly equipped 2027 GM HD trucks are rated for up to 20,000 pounds of conventional towing or 38,000 pounds with a gooseneck. Those are lineup maximums, not promises for every diesel Silverado or Sierra. Compare the actual cab, bed, drivetrain and hitch configurations before treating a higher torque figure as a higher tow rating.

GM’s supporting changes include rack-and-pinion electric power steering, electronic brake boost and 14.6-inch front brake rotors. They make a towing test more interesting than a simple horsepower contest. To decide which diesel truck works best, we need to compare acceleration under load, grade holding, exhaust braking and fuel use with comparable trucks and trailers.

What buyers still need to know

GM expects the updated HD trucks to reach U.S. dealers in late 2026, with the new diesel built in Brookville, Ohio. Pricing has not been announced. Until the diesel premium and comparable truck prices are available, the horsepower-per-dollar argument is incomplete.

Fuel consumption, DEF use, maintenance costs and long-term durability belong in this comparison as well. GM has not supplied a confirmed DEF-consumption comparison with the outgoing diesel. Nor can an all-new engine demonstrate years of customer reliability before buyers put it to work.

The early verdict is straightforward: GM takes the lead in rated engine output, Ford stays close on torque, and Ram’s Cummins remains a different six-cylinder alternative. The Duramax has won this round of the specifications contest. A towing test and real ownership costs will tell us whether it also wins the buying decision.