The GMC Sierra 3500HD, in its fifth generation (GMTT1XX), represents GMC’s heavy-duty full-size pickup truck offering. Produced from 2020 to 2023, the Double Cab Long Bed configuration with the 6.6-liter Duramax Turbo Diesel V8 engine producing 445 horsepower and paired with a 10-speed Allison automatic transmission, was a top-tier offering aimed at buyers needing substantial towing and hauling capacity. This variant occupied the premium segment of the 3500HD lineup, positioned above the gasoline-powered options and the lower-output diesel trims.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD V (GMTT1XX) Double Cab Long Bed |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) 4WD DRW 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 | 8.3 kg/Hp, 119.8 Hp/tonne |
| Weight-to-torque ratio | 3 kg/Nm, 332.3 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 | 3713 kg (8185.76 lbs.) |
| Max. weight | 6350 kg (13999.35 lbs.) |
| Max load | 2637 kg (5813.59 lbs.) |
| Fuel tank capacity | 136 l (35.93 US gal | 29.92 UK gal) |
| Permitted trailer load with brakes (12%) | 9072 kg (20000.34 lbs.) |
| Length | 6514 mm (256.46 in.) |
| Width including mirrors | 2457 mm (96.73 in.) |
| Height | 2037 mm (80.2 in.) |
| Wheelbase | 4127 mm (162.48 in.) |
| Front track | 1731 mm (68.15 in.) |
| Rear track | 1905 mm (75 in.) |
| Ride height (ground clearance) | 264 mm (10.39 in.) |
| Drivetrain Architecture | All wheel drive (4×4). ICE drives rear wheels, front wheels 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, 355×40 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Electric Steering |
| Tires size | 235/80 R17; 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 |
INTRODUCTION
The 2020-2023 GMC Sierra 3500HD Double Cab Long Bed equipped with the 6.6L Duramax diesel and 10-speed Allison automatic transmission represents a significant evolution in GMC’s heavy-duty truck offerings. Built on the GMTT1XX platform, this generation aimed to provide a more refined and capable experience than its predecessors. The Double Cab configuration offered increased rear passenger space compared to the standard cab, while the long bed provided ample cargo capacity. This particular variant was targeted towards customers who required a powerful and versatile truck for demanding tasks such as towing large trailers, hauling heavy loads, and navigating challenging terrain.
Powertrain & Engine Architecture
At the heart of this Sierra 3500HD lies the Duramax L5P 6.6-liter turbocharged diesel V8 engine. This engine is a cornerstone of GMC’s heavy-duty lineup, known for its robust construction and impressive torque output. The L5P utilizes a cast iron block, aluminum cylinder heads, and a variable geometry turbocharger to deliver 445 horsepower at 2800 rpm and a massive 910 lb-ft of torque at 1600 rpm. The engine employs a high-pressure common rail direct fuel injection system, enabling precise fuel delivery and optimized combustion. The overhead valve (OHV) valvetrain contributes to the engine’s durability and low-end torque characteristics. Paired with the engine is the Allison 10-speed automatic transmission, a heavy-duty unit designed to handle the engine’s substantial power and torque. This transmission features electronically controlled shifts and a wide gear ratio spread, optimizing both fuel efficiency and towing performance.
Driving Characteristics
The combination of the 445 hp Duramax engine and the 10-speed Allison transmission delivers a commanding driving experience. The truck exhibits strong acceleration, even when heavily loaded. The 10-speed transmission allows the engine to operate within its optimal power band more frequently, resulting in responsive performance in various driving situations. Compared to the gasoline-powered Sierra 3500HD models, the diesel variant offers significantly more low-end torque, making it ideal for towing and hauling. While the gasoline engines might feel more nimble in everyday driving, the Duramax provides a level of effortless power that is unmatched. Compared to the 6.6L Duramax with lower horsepower ratings, this variant offers a noticeable increase in overall performance, particularly when accelerating with a load. The Allison transmission’s smooth and precise shifts contribute to a refined driving experience, minimizing gear hunting and maximizing efficiency.
Equipment & Trim Levels
The Sierra 3500HD Double Cab Long Bed with the Duramax engine typically came standard with a comprehensive suite of features. These included 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 front seats, a premium sound system, and advanced safety technologies. Optional extras included a power sunroof, a navigation system, and a variety of trailering packages designed to enhance towing capabilities. The interior design focused on functionality and durability, with comfortable seating and intuitive controls.
Chassis & Braking
The Sierra 3500HD features a robust chassis designed to withstand the stresses of heavy-duty use. The front suspension utilizes coil springs and a double wishbone configuration, while the rear suspension employs a traditional leaf spring setup. This combination provides a comfortable ride while maintaining excellent load-carrying capacity. The braking system consists of ventilated disc brakes on all four wheels, providing ample stopping power even when towing a heavy trailer. An Anti-lock Braking System (ABS) is standard, enhancing safety and control during emergency braking situations. The truck’s heavy-duty frame and suspension components contribute to its overall stability and durability.
Market Reception & Comparison
The GMC Sierra 3500HD with the Duramax diesel engine consistently received positive reviews from automotive critics. The engine was praised for its power, torque, and refinement, while the Allison transmission was lauded for its smooth shifting and durability. Fuel economy, while not a primary concern for heavy-duty truck buyers, was considered competitive within the segment. Compared to the Ford Super Duty and Ram 3500, the Sierra 3500HD was often cited as offering a more refined interior and a more comfortable ride. However, some critics noted that the Sierra’s styling was less aggressive than that of its competitors. Reliability ratings for the Duramax engine and Allison transmission have generally been positive, although diesel engines can be more expensive to maintain than gasoline engines.
Legacy
The 2020-2023 GMC Sierra 3500HD with the 6.6L Duramax and 10-speed Allison transmission has established itself as a reliable and capable heavy-duty truck. The Duramax L5P engine has proven to be a durable and long-lasting powerplant, and the Allison transmission is renowned for its robustness. On the used car market, these trucks command a premium price due to their proven performance and towing capabilities. The combination of power, refinement, and durability makes this variant a popular choice among buyers who require a heavy-duty truck for work or recreational purposes. The GMTT1XX platform represents a significant step forward in GMC’s heavy-duty truck offerings, setting a high standard for performance and capability.
