The GMC Sierra 2500HD V (GMTT1XX) Crew Cab Long Bed, equipped with the 6.6-liter Duramax TD V8 engine producing 445 horsepower and paired with an Allison 10-speed automatic transmission, represents a significant iteration in GMC’s heavy-duty truck lineup. Produced from 2020 to 2023, this variant occupied a premium position within the Sierra 2500HD range, targeting buyers requiring substantial towing capacity and robust performance for demanding tasks. It builds upon the foundation of the GMTT1XX platform, a chassis designed for enhanced strength and capability compared to its predecessors.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD V (GMTT1XX) Crew Cab Long Bed |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) Automatic |
| Start of production | 2020 |
| End of production | 2023 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 7.7 kg/Hp, 129.1 Hp/tonne |
| Weight-to-torque ratio | 2.8 kg/Nm, 358.1 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 | 3446 kg (7597.13 lbs.) |
| Max. weight | 4990 kg (11001.07 lbs.) |
| Max load | 1544 kg (3403.94 lbs.) |
| Fuel tank capacity | 136 l (35.93 US gal | 29.92 UK gal) |
| Permitted trailer load with brakes (12%) | 8392 kg (18501.19 lbs.) |
| Length | 6759 mm (266.1 in.) |
| Width including mirrors | 2079 mm (81.85 in.) |
| Height | 2023 mm (79.65 in.) |
| Wheelbase | 4369 mm (172.01 in.) |
| Front track | 1731 mm (68.15 in.) |
| Rear (Back) track | 1736 mm (68.35 in.) |
| Ride height (ground clearance) | 256 mm (10.08 in.) |
| Drivetrain Architecture | Rear wheel drive. Internal Combustion engine (ICE) drives the rear wheels. |
| 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, a mainstay of GMC’s heavy-duty lineup, 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’s turbocharger, coupled with an intercooler, provides increased air density for enhanced power output. The overhead valve (OHV) valvetrain, while a more traditional design, is known for its durability and reliability. The Allison 10-speed automatic transmission is a crucial component, designed to handle the engine’s substantial torque output and provide smooth, efficient shifting. This transmission features electronically controlled shifts and a wide gear ratio spread, optimizing performance for both towing and everyday driving.
Driving Characteristics
The 445 horsepower and 910 lb-ft of torque delivered by the Duramax engine and Allison transmission combination translate into impressive real-world performance. While not designed for outright speed, this Sierra 2500HD excels at accelerating with heavy loads. The 10-speed automatic transmission allows the engine to remain within its optimal power band, even when towing. Compared to the gasoline-powered variants of the 2500HD, the diesel offers significantly more low-end torque, making it ideal for hauling and challenging terrain. The gear ratios are tuned for maximizing towing capacity, meaning that acceleration from a standstill without a load might feel less spirited than in lighter-duty trucks. The ride quality, even unladen, is generally comfortable for a heavy-duty truck, thanks to the tuned suspension.
Equipment & Trim Levels
The Crew Cab Long Bed configuration, combined with the Duramax engine, typically came in higher trim levels such as SLE, AT4, and Denali. Standard features generally included a large infotainment touchscreen with Apple CarPlay and Android Auto compatibility, a premium sound system, and a suite of driver-assistance technologies like automatic emergency braking and lane departure warning. Higher trims, like the Denali, added luxurious appointments such as leather upholstery, heated and ventilated seats, and a more refined interior finish. Optional extras included a power sunroof, a rear-seat entertainment system, and various towing packages.
Chassis & Braking
The GMTT1XX platform features a fully boxed frame constructed from high-strength steel, providing a solid foundation for heavy-duty use. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs a traditional leaf spring setup. This configuration balances ride comfort with load-carrying capacity. Braking duties are handled by ventilated disc brakes at all four corners, providing ample stopping power even when heavily loaded. The ABS system helps maintain control during emergency braking situations. The rear axle ratio is typically chosen to optimize towing performance, and can vary depending on the specific configuration.
Market Reception & Comparison
The GMC Sierra 2500HD with the Duramax diesel and Allison transmission consistently received positive reviews for its towing capability, robust performance, and comfortable ride. Critics praised the engine’s power and efficiency, as well as the transmission’s smooth operation. Compared to the gasoline-powered Sierra 2500HD models, the diesel variant offered superior fuel economy when towing heavy loads, although the initial purchase price was significantly higher. Compared to competitors like the Ford Super Duty and Ram 2500, the Sierra 2500HD was often seen as a well-rounded offering, balancing capability, comfort, and technology.
Legacy
The Duramax L5P engine and Allison 10-speed transmission have proven to be a reliable and durable powertrain combination. These trucks, even with significant mileage, continue to command strong resale values in the used car market. The L5P engine is known for its longevity, provided it receives regular maintenance, including oil changes and fuel filter replacements. The Allison transmission is also highly regarded for its robustness. The GMTT1XX platform, while superseded by newer generations, remains a capable and dependable choice for buyers seeking a heavy-duty truck with proven performance and towing capacity.
