GM announced the Duramax 8.3L turbo-diesel V8 on September 24, 2026, and it goes into the 2027 Chevrolet Silverado HD and GMC Sierra HD. According to GM, the new engine makes 555 horsepower and 1,230 lb-ft of torque. The company also says the first trucks should reach U.S. dealers beginning late 2026.

The engine is only part of the story, though. At the same time, GM paired it with new steering, new brakes and a new off-road mode, and it updated the gas V8 as well. GM has not announced pricing yet. Here are seven details from GM’s release, each checked against the company’s own text.

1. 555 hp and 1,230 lb-ft From the Duramax 8.3L

First, the headline numbers. GM rates the Duramax 8.3L at 555 hp and 1,230 lb-ft, and it calls both figures best in class for diesel horsepower and torque. However, that claim belongs to GM, so read it as the maker’s own comparison.

For context, Motor1 reports the outgoing 6.6-liter Duramax made 470 hp and 975 lb-ft. By the same report, Ford’s Power Stroke is rated at 500 hp and 1,200 lb-ft. Motor1 also calls the new engine “The Mongoose,” though GM’s release does not use that name. Inside, GM describes a compacted graphite iron block, a forged crankshaft and rods, steel pistons and a variable-geometry turbocharger.

2. Built in Brookville, Ohio

Next comes the factory. According to GM’s Duramax 8.3L announcement, the engine will be built at the expanded DMAX facility in Brookville, Ohio. GM says the plant covers 1.4 million square feet and handles both machining and assembly.

The company also says it previously invested $920 million to expand DMAX capacity for this engine program. In other words, the diesel comes from a plant GM enlarged specifically to build it.

3. An Allison 10-Speed Behind It

Meanwhile, the gearbox carries over by name. GM pairs the new diesel with the Allison 10L1000 10-speed automatic. The updated 6.6-liter gas V8 also uses the same transmission.

GM says new shift logic keeps each engine in its best range. As a result, the company promises smoother acceleration, stronger grade performance and more control with heavy trailers. Still, those are GM’s own claims, and the release gives no shift-time figures to back them with numbers.

4. A 38,000-Pound Gooseneck Rating

Towing is where heavy-duty buyers look first. GM lists up to 20,000 pounds of conventional trailering on properly equipped trucks. With a gooseneck hitch, however, the rating rises to 38,000 pounds.

In addition, GM quotes a gross combined weight rating of up to 46,500 pounds on select configurations. That figure covers the truck, its load and the trailer together. Motor1’s report repeats the same 20,000-pound and 38,000-pound figures.

5. Electric Rack-and-Pinion Steering

For 2027, GM switches its HD trucks to rack-and-pinion electric power steering. The company calls it a segment first for heavy-duty pickups. GM says it gives about 30% more steering output than its current hydraulic systems.

Because it is electric, the setup also drops the hydraulic pump, hoses and fluid. Alongside it, GM adds what it calls a segment-first electronic brake-boost system. According to the release, the trucks also get larger 14.6-inch front rotors with four-piston fixed calipers.

6. A One-Pedal Terrain Mode

Off the pavement, GM adds Terrain Mode. The company calls it a first for its HD trucks. It works in 4HI and 4LO. Once the driver lifts off the accelerator, the truck applies the brakes automatically.

As a result, a driver can crawl down a steep grade with one pedal. GM names the ZR2 and AT4X models in connection with the feature. Separately, the trucks offer up to 14 camera views, including Transparent Trailer View, Bed View and Surround Vision.

7. A Stronger 6.6L Gas V8, Too

Not every buyer wants a diesel, so GM updated the standard gas engine as well. The enhanced 6.6-liter gas V8 makes 412 hp and 472 lb-ft. GM says that torque figure is best in class among standard 2027 HD gas engines.

GM builds this engine at its Tonawanda Engine Plant in New York. Changes include a revised lubrication system, an engine-mounted oil cooler and a digital oil-level display. Like the Duramax 8.3L, it drives through the Allison 10L1000, and GM expects both trucks at U.S. dealers beginning late 2026.

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This article was created with the help of AI and was reviewed and edited by Fast Lane Only editors before publication.