General Motors unveiled its 2027 heavy-duty pickups on Sept. 24, and the headline sits under the hood. The Chevrolet Silverado HD and GMC Sierra HD offer an all-new Duramax 8.3-liter turbodiesel V8 rated at 555 hp and 1,230 lb-ft, numbers GM calls best in class. The trucks also switch to electric power steering and electronic brake boost, both segment firsts, according to GM. They arrive at U.S. dealers beginning in late 2026; pricing comes later.
GM says more than 60 percent of heavy-duty buyers choose a diesel, which explains where the money went. This is GM's first clean-sheet HD diesel V8 designed, developed and built in-house.
A bigger Duramax replaces the 6.6
The 8.3-liter uses a compacted graphite iron block, a forged crankshaft and connecting rods, steel pistons, a variable-geometry turbocharger and a dual-stage air-to-water charge cooler. It pairs with the Allison 10-speed 10L1000 automatic and a stronger exhaust brake. GM builds it at its expanded DMAX plant in Brookville, Ohio, a 1.4-million-square-foot site that received a $920 million investment.
GM Authority reports that the new engine replaces the 6.6-liter L5P Duramax outright rather than sitting above it. That L5P made 470 hp and 975 lb-ft, so the gain is 85 hp and 255 lb-ft. The standard 6.6-liter gas V8, built in Tonawanda, New York, gets a new intake manifold, an engine-mounted oil cooler and a digital oil-level display. It now makes 412 hp and 472 lb-ft.
Heavy-duty engines, 2026 vs. 2027
| Engine | 2026 | 2027 |
|---|---|---|
| Duramax diesel | 6.6L V8: 470 hp / 975 lb-ft | 8.3L V8: 555 hp / 1,230 lb-ft |
| Gas | 6.6L V8: 401 hp / 464 lb-ft | 6.6L V8: 412 hp / 472 lb-ft |
2027 figures from General Motors. 2026 figures and the retirement of the 6.6L Duramax as reported by GM Authority.
Electric steering and new brakes for heavy loads
The hydraulic steering gear gives way to a rack-and-pinion electric system that GM says delivers about 30 percent more output, along with less kickback and no pump, hoses or fluid to service. Assist no longer depends on engine speed. The brakes move to an electronic boost system with 14.6-inch front rotors and four-piston fixed front calipers, and GM says the system can flag brake fade or leaks sooner.
Drive modes are recalibrated for towing and off-road use. The Silverado HD ZR2 and Sierra HD AT4X get a new Terrain Mode, a first for GM's heavy-duty trucks, which allows one-pedal driving in 4HI and 4LO: lift off the accelerator and the truck brakes itself on steep grades.
“For 2027, we took GM’s proven HD validation playbook and turned up the capability,” said Mark Dickens, executive chief engineer for GM full-size trucks and SUVs. “HD customers don’t hold back — and neither did we.”
Towing ratings and what buyers should know
Properly equipped trucks are rated for up to 20,000 pounds with a conventional hitch and 38,000 pounds with a gooseneck, with a gross combined weight rating of up to 46,500 pounds. GM says every diesel dually can tow 30,000 pounds or more. Up to 14 camera views are available, including Transparent Trailer View, along with trailer tire pressure and temperature monitoring.
GM has not announced MSRPs, and its best-in-class claims are based on its own reading of competitors' published figures. Buyers who specifically want the proven 6.6-liter Duramax will need a 2026 truck, based on GM Authority's reporting. Everyone else should wait for prices before deciding whether the larger diesel is worth its premium.