The GMC Sierra 3500HD, specifically the fifth generation (GMTT1XX) produced from 2020 to 2023, represents GMC’s heavy-duty full-size pickup truck offering. This variant, featuring a Regular Cab and Long Bed configuration paired with the 6.6-liter Duramax Turbo Diesel V8 engine producing 445 horsepower and a 10-speed Allison automatic transmission, was positioned as a work-focused, high-capability truck aimed at customers needing substantial towing and hauling capacity. It served as a core offering within the Sierra 3500HD lineup, slotting between the less-expensive gasoline engine options and the more luxurious Denali trims.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD V (GMTT1XX) Regular Cab Long Bed |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) 4WD SRW Automatic |
| Start of production | 2020 |
| End of production | 2023 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 2 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 7.7 kg/Hp, 130 Hp/tonne |
| Weight-to-torque ratio | 2.8 kg/Nm, 360.6 Nm/tonne |
| Power | 445 Hp @ 2800 rpm |
| Power per litre | 67.4 Hp/l |
| Torque | 1234 Nm @ 1600 rpm (910.15 lb.-ft. @ 1600 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Duramax L5P |
| Engine displacement | 6604 cm3 (403 cu. in.) |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 103 mm (4.06 in.) |
| Piston Stroke | 99 mm (3.9 in.) |
| Compression ratio | 16:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Diesel Commonrail |
| Engine aspiration | Turbocharger, Intercooler |
| Valvetrain | OHV |
| Engine oil capacity | 9.5 l (10.04 US qt | 8.36 UK qt) |
| Coolant capacity | 29.1 l (30.75 US qt | 25.6 UK qt) |
| Kerb Weight | 3422 kg (7544.22 lbs.) |
| Max. weight | 5352 kg (11799.14 lbs.) |
| Max load | 1930 kg (4254.92 lbs.) |
| Fuel tank capacity | 106 l (28 US gal | 23.32 UK gal) |
| Permitted trailer load with brakes (12%) | 6577 kg (14499.8 lbs.) |
| Length | 5982 mm (235.51 in.) |
| Width including mirrors | 2076 mm (81.73 in.) |
| Height | 2056 mm (80.94 in.) |
| Wheelbase | 3595 mm (141.54 in.) |
| Front track | 1731 mm (68.15 in.) |
| Rear track | 1736 mm (68.35 in.) |
| Ride height (ground clearance) | 285 mm (11.22 in.) |
| Drivetrain Architecture | All wheel drive (4×4). ICE drives rear wheels, front engaged via clutch. |
| Number of gears and type of gearbox | 10 gears, automatic transmission Allison |
| Front suspension | Coil spring, Double wishbone, Transverse stabilizer |
| Rear suspension | Rigid axle suspension, Leaf spring |
| Front brakes | Ventilated discs, 350×40 mm |
| Rear brakes | Ventilated discs, 360×34 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Electric Steering |
| Tires size | 265/70 R17; 245/75 R17; 265/70 R18; 265/60 R20 |
| Wheel rims size | 7.5J x 17; 8J x 18; 8.5J x 20 |
Powertrain & Engine Architecture
The heart of this Sierra 3500HD is the Duramax L5P 6.6-liter turbocharged diesel V8. This engine, a staple of GMC and Chevrolet heavy-duty trucks, utilizes a cast iron block and aluminum cylinder heads. The L5P features a common-rail direct fuel injection system, delivering fuel at extremely high pressures for optimized combustion. The engine employs an overhead valve (OHV) valvetrain, a design choice prioritizing durability and low-end torque. A single variable geometry turbocharger with an intercooler provides forced induction, boosting power and efficiency. The 10-speed Allison automatic transmission, a heavy-duty unit specifically designed for the truck’s torque output, is a key component. This transmission offers smooth shifting and optimized gear ratios for both towing and everyday driving. The transmission’s ten forward gears allow the engine to operate in its most efficient range more often, improving fuel economy and reducing noise.
Driving Characteristics
The 445 horsepower and massive 1234 Nm (910 lb-ft) of torque delivered by the Duramax engine and 10-speed Allison transmission translate into impressive real-world performance. While not a sports truck, the Sierra 3500HD with this powertrain offers strong acceleration, even when heavily loaded. The Allison transmission’s gear ratios are well-suited for towing, providing ample power for climbing hills and maintaining speed on the highway. Compared to the gasoline engine options, the diesel provides significantly more low-end torque, making it ideal for demanding tasks. Compared to higher-output Duramax variants (available in some trims), this 445 hp version offers a balance between power and fuel efficiency. The automatic transmission, while convenient, doesn’t offer the same level of control as a manual transmission, but it simplifies operation for drivers primarily focused on work tasks.
Equipment & Trim Levels
The Regular Cab Long Bed 3500HD with the Duramax engine typically came with a functional, work-oriented interior. Standard features included vinyl upholstery, a basic infotainment system with a touchscreen display, and air conditioning. Higher trim levels, such as the SLE or LT, added features like cloth or leather upholstery, upgraded infotainment systems with navigation, and additional convenience features. Optional extras included a trailer brake controller, a gooseneck hitch, and various towing packages. The Regular Cab configuration prioritized interior space for work tools and equipment over passenger comfort.
Chassis & Braking
The Sierra 3500HD’s chassis is built for heavy-duty use. It features a fully boxed frame constructed from high-strength steel. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs leaf springs. This setup provides a comfortable ride, even when the truck is loaded. Braking duties are handled by ventilated disc brakes at all four corners. An Anti-lock Braking System (ABS) is standard. Due to the truck’s weight and intended use, rear drum brakes were sometimes fitted on lower trim levels, while higher trims received rear disc brakes. The steering system is a rack-and-pinion setup with electric power steering, providing responsive handling.
Market Reception & Comparison
Critics generally praised the Sierra 3500HD’s Duramax diesel engine and Allison transmission combination for its power, towing capacity, and reliability. The 445 horsepower version was seen as a sweet spot, offering ample power without the higher cost of the more powerful variants. Fuel economy, while not exceptional, was considered reasonable for a heavy-duty truck. Compared to the gasoline engine options, the diesel offered significantly better fuel economy when towing. Compared to competitors like the Ford Super Duty and Ram 3500, the Sierra 3500HD was often praised for its comfortable ride and refined interior.
Legacy
The Duramax L5P engine and Allison 10-speed transmission have proven to be exceptionally durable and reliable powertrains. These trucks, even with high mileage, continue to command strong resale values, particularly those well-maintained and used primarily for towing. The GMTT1XX generation Sierra 3500HD represents a significant step forward in heavy-duty truck technology, offering a blend of power, capability, and refinement. The 6.6-liter Duramax diesel remains a popular choice for truck owners who prioritize longevity and towing performance, and well-maintained examples of this generation are expected to remain on the road for many years to come.
