GMC Sierra HD T1XX: 2020-Present Guide
The 2020-and-newer GMC Sierra HD is the fourth-generation Sierra 2500HD and 3500HD, built on GM's T1XX truck family (Wikipedia lists it as GMT1HG). It launched with the first AT4 HD, the MultiPro tailgate and a 10-speed Allison for the Duramax, then got a big 2024 refresh with 470 hp, AT4X and Denali Ultimate. For 2027, it adds an all-new 8.3-liter Duramax. Here's what changed year to year, what to check, and how it rates for safety.
2020+ GMC Sierra HD at a Glance
Model years 2020–present US model years
Platform T1XX family Shared with the Silverado HD
Refresh 2024 New face, cabin and more diesel power
Power range 401–555 hp 6.6 gas V8 to the 2027 8.3 Duramax
Max towing 36,000 lb 2024–2026 3500HD dually, fifth-wheel
Gearbox Allison 10-speed Diesel from 2020, gas from 2024
What Makes the 2020+ Sierra HD Different
GMC didn't just reskin the old K2XX for 2020. The HD got a new frame, a much bigger and squarer look than the Sierra 1500 and a long list of towing tech, including ProGrade Trailering with up to 15 camera views and a Transparent Trailer view that makes the trailer seem to disappear on screen.
Under the hood, you get two choices. The 6.6-liter gas V8 makes 401 hp and 464 lb-ft and, according to GM, skips cylinder deactivation and auto stop-start entirely. Meanwhile, the 6.6-liter Duramax diesel started at 445 hp and 910 lb-ft, paired with a 10-speed Allison automatic.
The 2024 refresh is the big dividing line. It brought a new front end and a far nicer cabin with a 13.4-inch touchscreen, while the Duramax jumped to 470 hp and 975 lb-ft and gas trucks finally got the 10-speed. As a result, a 2024 truck feels a lot more modern than a 2020.
- 470 hp2024+ Duramax
- 975 lb-ft2024+ Duramax torque
- 36,000 lb3500HD max fifth-wheel
- 15Trailering camera views
What we like
- Huge towing ratings, especially the 3500HD dually
- Gas V8 is simple, with no cylinder deactivation
- 2024-and-up cabins rival luxury SUVs
What to watch
- Diesel option and top trims get very expensive
- Early trucks carry several recalls
- Diesel emissions parts can be costly out of warranty
2020+ GMC Sierra HD Engines and Power
This Sierra HD has had two engines for most of its life, and the 2027 update adds a third. Because the diesel got stronger for 2024 and was replaced for 2027, the model year matters if you tow heavy.
| Engine | Years | Found in | Output |
|---|---|---|---|
| 6.6L V8 gas | 2020–2023 | All trims, 6-speed automatic | 401 hp / 464 lb-ft |
| 6.6L V8 gas | 2024–2026 | All trims, 10-speed automatic | 401 hp / 464 lb-ft |
| 6.6L V8 gas (updated) | 2027 | All trims, 10-speed automatic | 412 hp / 472 lb-ft |
| 6.6L Duramax turbodiesel V8 (L5P) | 2020–2023 | Optional, 10-speed Allison | 445 hp / 910 lb-ft |
| 6.6L Duramax turbodiesel V8 (L5P) | 2024–2026 | Optional, 10-speed Allison | 470 hp / 975 lb-ft |
| 8.3L Duramax turbodiesel V8 | 2027 | Optional, 10-speed Allison | 555 hp / 1,230 lb-ft |
One big refresh, one new diesel
2020+ Sierra HD Changes by Model Year
Most of this truck's changes came in two steps: the 2024 refresh and the 2027 powertrain update. In between, GMC mostly shuffled features and packages.
- 2020 All-new truck with the first AT4 HD, the six-function MultiPro tailgate, up to 15 trailering camera views and a 10-speed Allison for the 445-hp Duramax.
- 2021 Wireless Apple CarPlay and Android Auto arrive, the MultiPro tailgate becomes standard on SLE, and the Denali Black Diamond Edition joins the lineup.
- 2022 The base trim is renamed Pro, with a few color and wheel changes.
- 2023 Only minor changes, since the refresh was pushed back a year.
- 2024 Major refresh with a new front end, new interior, available 13.4-inch screen and 15-inch head-up display. In addition, the Duramax rises to 470 hp, gas trucks get the 10-speed, and AT4X and Denali Ultimate arrive.
- 2025 Cruise control and a trailer brake controller become standard on Pro, while adaptive cruise becomes standard on AT4 and Denali.
- 2026 Mostly a carryover. GMC drops some 2WD and Double Cab configurations, makes MultiPro optional on SLT and adds new paint colors.
- 2027 The 8.3-liter Duramax (555 hp) replaces the 6.6 diesel, the gas V8 gets 412 hp, and electric power steering and a new brake booster arrive. Max gooseneck towing rises to 38,000 lb.
Our verdict: if your budget allows, aim for a 2024 or newer truck. The refreshed cabin, 10-speed gas trucks and stronger diesel are the biggest upgrades this generation has had so far.
2020+ GMC Sierra HD Special Models
The 2020+ Sierra HD covers everything from a basic work truck to a luxury hauler, plus GMC's first heavy-duty AT4X.
2024–present
AT4X and AT4X AEV Edition
Multimatic DSSV dampers 35-in tires Gas or diesel
GMC's first HD AT4X gets a factory lift, rear locker, skid plates and 11.6 inches of ground clearance. The AEV Edition adds steel bumpers, a winch-ready front end and more armor, so it's built for trails, not just looks.
2024–present
Denali and Denali Ultimate
Luxury trims Massaging seats 15-in head-up display
Denali is the dressy HD, and Denali Ultimate goes further with full-grain leather, a microsuede headliner and 16-way massaging front seats. It started at $78,847 at launch for 2024.
2020–present
3500HD Dually
Dual rear wheels Fifth-wheel ready Up to 36,000 lb
If you pull a big fifth-wheel or gooseneck, this is the one. A 2026 3500HD dually is rated up to 36,000 lb fifth-wheel and over 7,000 lb of payload with the gas V8, and the 2027 truck is rated up to 38,000 lb.
2020+ GMC Sierra HD Recalls
The recalls you'll see most on a 2020+ Sierra HD involve the power tailgate and the diesel's 10-speed transmission software. Neither is something to ignore, because a tailgate that pops open can dump cargo, and the transmission issue can briefly lock the rear wheels.
| Model years | Campaign | What's affected |
|---|---|---|
| 2020–2024 | NHTSA 24V060000 | Power-release tailgate can open unexpectedly when water shorts the release switch. Dealers replace the switches with sealed parts. |
| 2024 | NHTSA 24V894000 | Expands the tailgate recall to more 2024 trucks with the power-release gate. Same fix. |
| 2020–2022 (Duramax) | NHTSA 24V797000 | A worn transmission control valve can fail on a downshift and briefly lock the rear wheels. New software detects the wear and limits the truck to fifth gear. |
| 2020 (Duramax) | NHTSA 26V083000 | Some trucks repaired under 24V797000 got the wrong software. Dealers inspect and reflash. |
| Early 2024 | NHTSA 23V549000 | Steering gear shaft on a small batch of trucks may not have been heat-treated correctly and can break. Dealers inspect and replace the gear. |
| 2020–2021 | NHTSA 20V792000 | Front center seat belt bracket may not be secured to the seat frame. Dealers inspect and fix it. |
2020+ GMC Sierra HD Safety Ratings by Region
Heavy-duty pickups like the Sierra 2500HD and 3500HD are heavier than the vehicles most crash-test programs cover, so this truck has almost no crash ratings. That doesn't mean it's unsafe, but you can't compare it with a Sierra 1500 on stars.
| Region | Program | Rating | What it means |
|---|---|---|---|
| United States | NHTSA | Not rated | NHTSA hasn't star-rated the 2020+ Sierra HD or its Silverado HD twin in frontal, side or rollover tests. |
| United States | IIHS | No crash ratings | IIHS hasn't crash-tested the Sierra HD, so there are no crashworthiness or headlight ratings. |
| United States | IIHS (commercial vehicles) | Partial / Marginal | In its 2026 commercial-vehicle program, IIHS rated the 2026 Sierra 3500 crew cab's vehicle-to-vehicle front crash prevention Partial and pedestrian front crash prevention Marginal, based on a 2025 Silverado 3500HD. |
| Canada | Transport Canada | Not rated | There's no separate Canadian crash rating for this truck. |
| Europe, Australia | Euro NCAP, ANCAP | Not rated | Neither program has tested the Sierra HD. |
Bottom line: check that the driver-assist features you want are on the truck you're buying, because many of them are optional or trim-dependent.
Buying a Used 2020+ GMC Sierra HD
A 2020+ Sierra HD is a tough truck, and the gas V8 in particular has a simple, proven design. Still, a few things come up again and again.
- Tailgate recall. Run the VIN and make sure the power-release tailgate fix (24V060000 or 24V894000) has been done.
- Diesel transmission software. On 2020–2022 Duramax trucks, confirm the 24V797000 software update is done, and on affected 2020 trucks the 26V083000 follow-up too.
- DEF system. GM has issued bulletins for failed DEF tank heaters on 2020–2021 diesels and erratic DEF level readings on 2020–2024 diesels. Watch for Service Emission System warnings and ask for repair records, because a DEF tank out of warranty is expensive.
- Steering shake on early trucks. Some 2020 trucks shake at highway speeds. GM's fix ranges from road-force balancing the tires to reprogramming the power steering, so a test drive at 50 to 80 mph tells you a lot.
Our picks
- Best overall: 2024–2026 Duramax
- Best value: 2020–2023 gas V8
- Best off-road: AT4X
Think twice
- Any truck with an open tailgate or transmission recall
- Diesels with emissions warnings and no records
- Heavily modified or deleted diesels
Other Sierra HD Generations
The 2020+ truck is the newest Sierra HD. Jump to the full list to see the older K2XX, GMT900 and GMT800 trucks.
2020+ GMC Sierra HD FAQ
What years is the current GMC Sierra HD generation?
The current Sierra HD covers the 2020 model year to today. It got a major refresh for 2024 and a powertrain update for 2027, but it's still the same generation.
What changed on the 2024 Sierra HD?
A new front end and interior, an available 13.4-inch touchscreen and 15-inch head-up display, a 470-hp Duramax, the 10-speed for gas trucks, and the new AT4X and Denali Ultimate trims.
How much horsepower does the Duramax in a Sierra HD have?
The 6.6-liter Duramax makes 445 hp and 910 lb-ft in 2020–2023 trucks and 470 hp and 975 lb-ft from 2024. The 2027 truck's new 8.3-liter Duramax makes 555 hp and 1,230 lb-ft.
Does the 6.6 gas V8 have cylinder deactivation?
No. GM confirmed the 6.6-liter gas V8 in the HD has no cylinder deactivation and no auto stop-start, and it runs on regular 87-octane gas.
How much can a 2026 Sierra 2500HD tow?
With the Duramax, up to 20,000 lb on a ball hitch and about 22,400 lb fifth-wheel or gooseneck. The gas 2500HD is rated up to 16,000 lb conventional.
Is the 2027 Sierra HD a new generation?
No. The 2027 truck keeps the current body and cab but adds the 8.3-liter Duramax, an updated gas V8 and electric power steering. GM Authority expects the next-generation Sierra HD around the 2029 model year.
Sources
- GM Authority: 2020 Sierra HD revealed
- GM Authority: 6.6L L8T has no AFM or stop-start
- Edmunds: 2024 Sierra HD and Denali Ultimate
- GM News: Sierra HD AT4X and AEV Edition
- GM Authority: 2026 Sierra HD towing
- Equipment World: 2027 Sierra HD revealed
- The Drive: 8.3L Duramax specs
- NHTSA recall 24V-060 report
- GM Authority: rear-wheel lock-up recall
- IIHS: 2026 Sierra 3500 crew cab
- GM TechLink: DEF tank heater bulletin
- GM TechLink: steering wheel shake
Keep Exploring
See every Sierra HD generation side by side, or head back to the full GMC lineup.
Photo credits
- Header image: deathpallie325, CC BY-SA 4.0, cropped and resized.
- Silver 2024 GMC Sierra 2500HD AT4X crew…: HJUdall, CC0, cropped and resized.
- Rear view of a black 2024 GMC…: deathpallie325, CC BY-SA 4.0, cropped and resized.
- White 2023 GMC Sierra 3500HD Denali dually…: HJUdall, CC0, cropped and resized.
- White 2020 GMC Sierra 2500HD with the…: DestinationFearFan, CC BY-SA 4.0, cropped and resized.