2027 GMC Sierra HD
A new diesel, new brakes and a late-2026 arrival.
On September 24, 2026, GM pulled the cover off its 2027 Sierra HD trucks, the 2500HD and the 3500HD. If you pull something heavy across the Mid-South, this is the page to bookmark. Everything below comes from GM's own release and the GMC website, and where GM has said nothing yet, we tell you that too.
Five Things to Know Right Now
GM calls the 2027 changes updates, and the word redesign shows up in neither the release nor the GMC page. The updates are big ones all the same, and most of them are under the hood and under your foot.
| Item | Where It Stands | What We Know |
|---|---|---|
| Timing | Expected | GM expects these trucks to start reaching showrooms in late 2026. It has not given a build-start or order-open date. |
| Diesel | Announced | A brand-new 8.3-liter Duramax V8 rated at 555 horsepower and 1,230 lb-ft of torque. |
| Gas | Announced | The 6.6-liter V8 stays as the standard engine, reworked, at 412 horsepower and 472 lb-ft. |
| Towing | Announced | The 3500HD tops out at 38,000 lb and the 2500HD at 23,100 lb, both with the right equipment. |
| Price | Not Out | GM has promised an MSRP in a later update, and we will not guess at it. |
Two Engines, Two Different Jobs
Allison's 10-speed automatic, model 10L1000, backs up both engines.
Duramax 8.3L Turbo-Diesel V8
555 hp · 1,230 lb-ftGM had never started a heavy-duty V8 from a blank sheet before this one. The company drew it up, engineered it and builds it at its own diesel plant in Brookville, Ohio. The block is compacted graphite iron. Crank and rods are forged and the pistons are steel. Charge air gets cooled in two stages by water, a variable-geometry turbo handles boost, and the exhaust brake and aftertreatment layout are both new.
GM calls the output best in class for a diesel. Its own footnote says that measures against the latest competitor data GM has, leaves out GM's other vehicles and follows SAE J1349. On gmc.com, the Denali Ultimate is the trim listed with this engine.
Enhanced 6.6L V8 Gas
412 hp · 472 lb-ftGM reworked the standard gas engine. The intake is a new Turbo-Jet design, oiling has been revised, an oil cooler now mounts to the engine itself and the oil level shows on a digital readout. GM builds it in Tonawanda, New York.
GM says the torque figure is the best among standard gas engines in the 2027 heavy-duty class.
What Can It Pull?
| Setup | GM's Top Figure |
|---|---|
| Sierra 2500HD, max available | 23,100 lb |
| Sierra 3500HD, max available | 38,000 lb |
| Diesel dually, every one | 30,000 lb or more, available |
| Conventional hitch | Up to 20,000 lb |
| Gooseneck | Up to 38,000 lb |
| Gross combined weight rating | Up to 46,500 lb |
Read those as ceilings. GM attaches "properly equipped" and "select configurations" to them, and it has not released towing tables by engine or cab. When it does, we will build the list for you here. Until then, a real number for your trailer means a conversation about the exact truck.
Steering, Brakes and Trailer Help
| System | What It Means for You |
|---|---|
| Steering | Hydraulic assist is gone. A rack-and-pinion electric setup replaces it, which GM says is a first in the segment. GM puts it at roughly 30 percent more power than the hydraulic gear on today's HD trucks, and the help no longer rises and falls with engine speed. |
| Brakes | Another segment first from GM: electronic brake-boost, which the GMC site calls eBoost. Up front you get 14.6-inch rotors clamped by four-piston fixed calipers, and the rear hardware is upgraded. The system works alongside adaptive cruise and automatic emergency braking. |
| Drive Modes | Choose from Normal, Tow/Haul or Off-Road. New on the AT4X is Terrain Mode, one-pedal driving off-road in 4HI and 4LO, and GM says no heavy-duty truck of theirs has offered that before. |
| Trailer Help | You can order up to 14 camera views, among them a see-through trailer view, a look into the bed and surround vision. Also on the available list: a trailering app, blind-zone alert for the trailer's sides, trailer tire pressure and temperature readouts, and ProGrade. Adaptive cruise works with a trailer hooked up. |
| Screens | Available hardware is a 13.4-inch infotainment display, a 12.3-inch driver display and a multicolor head-up display that measures 15 inches. |
Seven Ways to Build One
| Trim | What You Get |
|---|---|
| Pro | The work-first entry. It runs the gas 6.6L with the Allison, plus adaptive cruise that can manage a trailer, a trailering package, and both a trailer brake controller and towing mirrors. |
| SLE | Brings in the big screens, Traction Select with a Tow/Haul setting and 18-inch machined wheels. |
| SLT | Adds a heated wheel and available power bucket seats that heat and ventilate, plus ProGrade trailering with the in-vehicle app. |
| AT4 | Jet Black cabin with Kalahari accents, gloss black 20-inch wheels and an off-road suspension package with skid plates. All-terrain BFGoodrich tires are available. |
| AT4X | Sits 1.5 inches taller from the factory, with Multimatic DSSV dampers, a rear electronic locker, 35-inch Goodyear Territory tires, skid plates, massaging seats and Terrain Mode. |
| Denali | Real wood and patterned aluminum inside, Forge leather, Ultra-Bright 20-inch wheels and heated, ventilated power seats. |
| Denali Ultimate | The top of the lineup. This is where gmc.com lists the 8.3L diesel, alongside a Vader Chrome grille, an Alpine Umber cabin in Paldao wood and full-grain leather, and power seats that massage. |
What GM Has Not Told Us Yet
When we read GM's release and the GMC page on September 29, 2026, these were missing:
- The MSRP.
- A build-start or order-open date.
- Fuel economy.
- Payload.
- Towing tables by engine and by cab.
We would rather leave a gap than fill it with a rumor. This page gets updated as GM fills those in.
Can't Wait Until Late 2026?
See current stock on the Sierra 2500 and Sierra 3500 pages, or look at the half-ton on our 2027 Sierra 1500 page. One Price. One Person. One Hour.
Sierra HD Questions, Answered
Has GM really announced a 2027 Sierra HD?
Yes. GM published the announcement on September 24, 2026, and GMC lists the truck on its site under Future Vehicles.
How soon can I get behind the wheel of one?
GM says dealers should start seeing them in late 2026. It has not named a day, so we will not either.
How much power does the new diesel make?
The new Duramax 8.3L diesel is rated at 555 horsepower and 1,230 lb-ft of torque, and it works with an Allison 10-speed.
What will a 3500HD pull?
GM's top figure for the 3500HD is 38,000 lb, and the 2500HD tops out at 23,100 lb. Both assume the right equipment and specific configurations.
Is this a full redesign?
GM's own word is updates. The new list: the diesel, a reworked gas V8, steering that runs on electricity, brake-boost handled electronically, and more trailering technology.
What is the price?
There is no price yet. GM has promised an MSRP in a later update.
Which trim comes with the 8.3L?
On gmc.com, the Denali Ultimate is the trim listed with the Duramax 8.3L. We have not found it listed on another trim, so confirm with us first.
More From Rivard-Royall GMC
Rivard-Royall GMC · 2621 Mendenhall Rd S, Memphis, TN 38115 · Sales: 901-881-0179