GMC Sierra HD
GMC Sierra HD is the heavy-duty side of GMC's pickup lineup: the 2500HD and 3500HD trucks you buy when a half-ton Sierra 1500 isn't enough. The HD name arrived for 2001 along with the Duramax diesel and Allison automatic, and it's since added Denali luxury, AT4 and AT4X off-road trims and towing ratings up to 36,000 lb. It shares its bones with the Chevrolet Silverado HD, but GMC gives it its own styling, cabins and trims. Pick your year below to jump to the right generation, or read on for the history and which one suits you.
GMC Sierra HD at a Glance
HD name since 2001 Arrived with the first Duramax
Generations 4 GMT800 to today's T1XX-based truck
Body styles 2500HD, 3500HD Single or dual rear wheels on the 3500HD
Current power 401–470 hp 6.6 gas V8 to 6.6 Duramax
Max towing 36,000 lb 2026 3500HD dually, fifth-wheel
Twin Chevy Silverado HD Same chassis, GMC styling and trims
GMC Sierra HD Generations
Years shown are US model years. The 2007 model year overlaps because GMC sold the old GMT800 truck as the 2007 Sierra Classic HD while the new GMT900 truck arrived midyear as a 2007.5. Codes are GM's platform names that owners use, and Wikipedia lists today's truck as GMT1HG on the T1XX family. Before 2001, GMC's heavy-duty 2500 and 3500 pickups were sold as Sierra C/K trucks without the HD name. Pick a card to open its full guide.
2001–2007
First Sierra HD
GMT8007 model years
The first truck called Sierra HD, launched with the 300-hp Duramax diesel and Allison five-speed. The 2006 LBZ diesel added power and a six-speed.
Guide coming soon
2007–2014
Second gen
GMT9008 model years
Arrived as a 2007.5 model with a cleaner LMM Duramax. The first Sierra Denali HD followed for 2011 with a 397-hp LML diesel.
Guide coming soon
2015–2019
Third gen
K2XX5 model years
Added driver-assist tech and the All Terrain HD. The 445-hp L5P Duramax and the All Terrain X arrived for 2017.
Guide coming soon
2020–present
Fourth gen
T1XX7 model years
Today's Sierra HD, with AT4, the MultiPro tailgate and a 10-speed Allison. The 2024 refresh brought 470 hp, AT4X and Denali Ultimate.
Read the T1XX guide →
GMC Sierra HD History
The Sierra HD went from a workhorse with a new diesel to a $90,000-plus luxury tow rig. Here are the moments that shaped it.
- 1988 The GMT400 trucks arrive, and GMC starts selling its full-size pickups, heavy-duty 2500 and 3500 models included, under the Sierra name.
- 2001 The GMT800 Sierra HD launches with the 6.6-liter Duramax diesel (300 hp / 520 lb-ft) and the Allison 1000 five-speed automatic.
- 2006 The LBZ Duramax makes 360 hp and 650 lb-ft, and the Allison gains a sixth gear.
- 2007 The GMT900 truck arrives midyear as a 2007.5 model with the 365-hp LMM Duramax.
- 2011 The first Sierra Denali HD brings GMC's luxury trim to heavy duty, with a 397-hp, 765 lb-ft LML Duramax.
- 2015 The K2XX HD launches with adaptive cruise, forward collision alert and lane departure warning, plus an All Terrain HD package.
- 2017 The L5P Duramax arrives with 445 hp and 910 lb-ft, along with the All Terrain X.
- 2020 An all-new HD brings the first AT4, the six-function MultiPro tailgate, 15 trailering camera views and a 10-speed Allison for the diesel.
- 2024 A big refresh adds a new face and cabin, a 470-hp, 975 lb-ft Duramax, the 10-speed for gas trucks, AT4X and Denali Ultimate.
- 2027 GMC reveals an updated Sierra HD with an all-new 8.3-liter Duramax V8 rated at 555 hp and 1,230 lb-ft, plus electric power steering.
Which Sierra HD Generation Is Right for You?
The right Sierra HD depends on what you tow, how much tech you want and your budget. Here's how the generations line up for most buyers.
| Generation | Years | Best for |
|---|---|---|
| GMT800 | 2001–2007 | Budget diesel trucks; the 2006–2007 LBZ is the favorite |
| GMT900 | 2007–2014 | Solid value; the 2011–2014 LML trucks are stronger but have the CP4 fuel pump |
| K2XX | 2015–2019 | More safety tech; the 2017–2019 L5P diesel is the one to find |
| T1XX | 2020–present | Highest towing, best cameras and cabins; 2024 and up for the newest tech |
Our take: for most used buyers, a 2017–2019 K2XX with the L5P or a 2024-and-newer T1XX truck is the sweet spot. Either way, check recall history and diesel emissions repairs before you buy.
Sierra HD Owners Community
Sierra HD owners talk towing setups, fifth-wheel and gooseneck hitches, diesel maintenance and keeping high-mileage trucks working. Share your truck, ask questions and swap tips with other owners.
- Fifth-wheel and gooseneck towing setups
- Duramax diesel vs 6.6 gas V8
- DEF and emissions system repairs
- AT4 and AT4X off-road builds
- Leveling kits, wheels and tires
- Recalls and dealer service experiences
- Real-world fuel economy while towing
- LB7 and LBZ Duramax restorations
GMC Sierra HD FAQ
What years is each GMC Sierra HD generation?
In the US: GMT800 2001–2007, GMT900 2007.5–2014, K2XX 2015–2019 and the current T1XX-based truck from 2020 on. The 2024 refresh and the 2027 update are part of the current generation.
What's the difference between the Sierra 2500HD and 3500HD?
The 3500HD has a stronger rear setup and comes with single or dual rear wheels, so it carries a lot more payload and has much higher fifth-wheel ratings. For 2026, the 3500HD dually is rated up to 36,000 lb fifth-wheel, while the 2500HD tops out around 22,400 lb.
Is the Sierra HD the same as the Silverado HD?
Mechanically, mostly yes. They share the frame, engines and transmissions, but GMC uses its own sheet metal, interiors and trims like Denali, AT4 and AT4X.
How much can a GMC Sierra HD tow?
A 2026 Sierra HD with the Duramax can pull up to 20,000 lb on a ball hitch, and a 3500HD dually is rated up to 36,000 lb with a fifth-wheel. Your exact rating depends on cab, bed, axle and engine, so check the door-jamb label and GMC's towing guide.
What engine does the 2027 Sierra HD get?
GMC says the 2027 Sierra HD swaps the 6.6-liter Duramax for a new 8.3-liter Duramax V8 with 555 hp and 1,230 lb-ft. The 6.6-liter gas V8 stays, updated to 412 hp and 472 lb-ft.
Where is the GMC Sierra HD built?
Current Sierra HD trucks are built at GM's Flint Assembly plant in Michigan.
Keep Exploring
Explore GMC's full lineup, or see how Ford, Chevrolet and Ram trucks stack up against the Sierra HD.
Photo credits
- Header image: Kevauto, CC BY-SA 4.0, cropped and resized.
- Black GMT800 GMC Sierra 2500HD Classic SLT…: HJUdall, CC0, cropped and resized.
- Black 2012 GMC Sierra Denali HD (GMT900)…: Bull-Doser, Public domain, cropped and resized.
- Black K2XX GMC Sierra Denali HD crew…: Bull-Doser, Public domain, cropped and resized.
- White 2024 GMC Sierra 2500HD SLE regular…: HJUdall, CC0, cropped and resized.