The GMC Sierra 2500HD V (GMTT1XX) Double Cab Long Bed, equipped with the 6.6-liter Duramax TD V8 engine producing 445 horsepower, represents a significant iteration in GMC’s heavy-duty truck lineup. Produced from 2020 to 2023, this variant occupied a premium position within the 2500HD series, targeting buyers requiring substantial towing and hauling capabilities combined with a degree of refinement. It builds upon the foundation of the GMTT1XX platform, a robust chassis designed for demanding workloads, and caters to the North American market’s preference for powerful, full-size pickup trucks.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD V (GMTT1XX) Double Cab Long Bed |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) Automatic |
| Start of production | 2020 year |
| End of production | 2023 year |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 7.6 kg/Hp, 131.9 Hp/tonne |
| Weight-to-torque ratio | 2.7 kg/Nm, 365.7 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 | 29.1 l, 30.75 US qt | 25.6 UK qt |
| Kerb Weight | 3374 kg, 7438.4 lbs |
| Max. weight | 4944 kg, 10899.65 lbs |
| Max load | 1570 kg, 3461.26 lbs |
| Fuel tank capacity | 136 l, 35.93 US gal | 29.92 UK gal |
| Permitted trailer load with brakes (12%) | 6577 kg, 14499.8 lbs |
| Length | 6514 mm, 256.46 in |
| Width including mirrors | 2079 mm, 81.85 in |
| Height | 2027 mm, 79.8 in |
| Wheelbase | 4127 mm, 162.48 in |
| Front track | 1731 mm, 68.15 in |
| Rear (Back) track | 1736 mm, 68.35 in |
| Ride height (ground clearance) | 258 mm, 10.16 in |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels of the vehicle. |
| Drive wheel | Rear wheel drive |
| 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 | Cone worm with recirculation balls |
| Power steering | Hydraulic 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 2500HD is the Duramax L5P 6.6-liter turbocharged diesel V8. This engine represents a significant evolution of the Duramax design, incorporating technologies to enhance both power and efficiency. The L5P utilizes a cast iron block and aluminum cylinder heads, contributing to its durability. The engine employs a common-rail direct fuel injection system, delivering fuel at extremely high pressures for optimized combustion. A variable geometry turbocharger (VGT) and intercooler further enhance performance by increasing air intake and reducing intake air temperature. The engine’s overhead valve (OHV) valvetrain, while a traditional design, is known for its robustness and reliability. Paired with the engine is the Allison 10-speed automatic transmission, a heavy-duty unit specifically designed to handle the substantial torque output of the Duramax engine. This transmission features electronically controlled shifts and a lock-up torque converter for improved fuel economy.
Driving Characteristics
The 445 horsepower and 910 lb-ft of torque delivered by the Duramax engine and Allison transmission combination provide the Sierra 2500HD with exceptional towing and hauling capabilities. In real-world driving, the truck feels incredibly capable, even when fully loaded. The 10-speed automatic transmission is well-tuned, providing smooth and responsive shifts. While not as quick off the line as gasoline-powered trucks, the Duramax offers a broad torque curve, making it ideal for towing heavy trailers or navigating challenging terrain. Compared to the 6.6L gasoline engine option, the Duramax provides significantly more torque at lower RPMs, making it easier to maintain speed while towing. Compared to lighter-duty Sierra 1500 models, the 2500HD feels more substantial and planted, offering a more confident driving experience when carrying heavy loads.
Equipment & Trim Levels
The Double Cab Long Bed configuration offered a spacious interior with seating for five passengers. Standard equipment on this trim typically included features such as air conditioning, power windows and locks, a touchscreen infotainment system with Apple CarPlay and Android Auto compatibility, and a rearview camera. Higher trim levels, such as Denali, added premium features like leather upholstery, heated and ventilated seats, a premium sound system, and advanced safety technologies. Optional extras included a sunroof, navigation system, and various towing packages. The interior design focused on functionality and durability, with materials chosen to withstand the demands of heavy-duty use.
Chassis & Braking
The Sierra 2500HD utilizes a fully boxed frame constructed from high-strength steel, providing a solid foundation for the truck. The front suspension features coil springs and a double wishbone design, while the rear suspension employs leaf springs. This configuration is optimized for carrying heavy loads and maintaining stability. Braking duties are handled by ventilated disc brakes on all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) is standard. The truck’s robust chassis and braking system contribute to its overall stability and control, even when towing heavy trailers.
Market Reception & Comparison
The GMC Sierra 2500HD with the Duramax engine and Allison transmission was generally well-received by critics and consumers alike. It was praised for its powerful engine, smooth transmission, and comfortable ride. Fuel economy, while not a primary concern for heavy-duty truck buyers, was considered competitive within its class. Compared to other diesel-powered heavy-duty trucks, such as the Ford Super Duty and Ram 2500, the Sierra 2500HD offered a compelling combination of performance, refinement, and reliability. The Duramax engine was consistently ranked among the best diesel engines in the industry.
Legacy
The Duramax L5P engine paired with the Allison 10-speed automatic has proven to be a durable and reliable powertrain. These trucks have maintained strong resale values in the used car market, reflecting their reputation for longevity and capability. While diesel engines require specific maintenance procedures, such as regular diesel particulate filter (DPF) regeneration, the Duramax L5P has generally been considered a relatively trouble-free engine. The GMTT1XX platform Sierra 2500HD continues to be a popular choice for those seeking a capable and reliable heavy-duty truck, and the 6.6-liter Duramax remains a benchmark in the diesel engine world.
