The GMC Sierra 2500HD IV (GMTK2XX) Double Cab Long Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 445 horsepower, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2017 to 2019, this variant occupied a premium position within the Sierra 2500HD lineup, targeting buyers requiring substantial towing capacity and robust performance. It was part of the fourth generation of the Sierra HD series, built on the GMTK2XX platform, which focused on increased strength, refinement, and technology compared to its predecessors. This configuration, combining the powerful Duramax diesel with a four-wheel-drive system and automatic transmission, was a popular choice for both commercial and personal use, particularly in regions where heavy hauling and challenging terrain were common.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD IV (GMTK2XX) Double Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) 4WD Automatic |
| Start of production | 2017 |
| End of production | 2019 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 6.6 kg/Hp, 151.2 Hp/tonne |
| Weight-to-torque ratio | 2.4 kg/Nm, 419.3 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 | 29.7 l (31.38 US qt | 26.13 UK qt) |
| Kerb Weight | 2943 kg (6488.2 lbs.) |
| Max. weight | 4309 kg (9499.72 lbs.) |
| Max load | 1366 kg (3011.51 lbs.) |
| Trunk (boot) space – maximum | 2162 l (76.35 cu. ft.) |
| 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 | 6322 mm (248.9 in.) |
| Width including mirrors | 2045 mm (80.51 in.) |
| Height | 1977 mm (77.83 in.) |
| Wheelbase | 4017 mm (158.15 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Ride height (ground clearance) | 214 mm (8.43 in.) |
| Minimum turning circle (turning diameter) | 16.2 m (53.15 ft.) |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels permanently, and the front wheels are driven through an electrically or mechanically operated clutch if necessary. |
| Drive wheel | All wheel drive (4×4) |
| Number of gears and type of gearbox | 6 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 |
| Tires size | 245/75 R17; 265/70 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 improve both power and efficiency. The L5P utilizes a cast iron block and aluminum cylinder heads, contributing to its durability. The engine employs a high-pressure common rail direct fuel injection system, delivering fuel directly into the cylinders 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 OHV valvetrain, while traditional, is robust and well-suited for the demands of heavy-duty trucking. The Allison 1000 six-speed automatic transmission is paired with the Duramax engine. This transmission is renowned for its durability and ability to handle high torque outputs, making it an ideal match for the diesel engine. The 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 produced by the Duramax engine translate into impressive real-world performance. The Sierra 2500HD with this powertrain is capable of accelerating briskly, even when heavily loaded. The Allison transmission provides smooth and precise shifts, and the gear ratios are well-suited for both towing and everyday driving. Compared to lower-output gasoline engine options, the Duramax offers significantly more low-end torque, making it easier to pull heavy trailers and navigate challenging terrain. While not as quick off the line as a lighter gasoline-powered truck, the Duramax excels in situations requiring sustained power and pulling strength. The 4WD system provides excellent traction in various conditions, enhancing stability and control.
Equipment & Trim Levels
The Double Cab Long Box configuration offered a spacious interior with seating for five passengers. Standard features typically included air conditioning, power windows and locks, a basic infotainment system with a touchscreen display, and a rearview camera. Higher trim levels, such as the Denali, added premium features like leather upholstery, heated and ventilated front seats, a premium sound system, and advanced safety technologies. Optional extras included a navigation system, a sunroof, and various towing packages. The Double Cab configuration provided a larger rear seat area compared to the standard cab models, making it more comfortable for passengers on long trips.
Chassis & Braking
The GMTK2XX platform features a fully boxed frame constructed from high-strength steel, providing a solid foundation for the truck. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs leaf springs. This setup is designed to handle heavy loads and provide a comfortable ride. The braking system consists of ventilated discs on all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) is standard, enhancing safety and control during emergency braking situations. The rear axle ratios were typically chosen to optimize either fuel economy or towing capacity, depending on the specific configuration.
Market Reception & Comparison
The GMC Sierra 2500HD with the 6.6-liter Duramax diesel engine and Allison transmission was generally well-received by critics and consumers alike. It was praised for its powerful engine, smooth transmission, and robust construction. Fuel economy, while not exceptional, was considered reasonable for a heavy-duty truck of its size and capability. Compared to the gasoline engine options, the Duramax offered superior towing capacity and fuel efficiency when hauling heavy loads. The Duramax/Allison combination was often seen as the benchmark in the heavy-duty truck segment, setting a high standard for performance and reliability.
Legacy
The Duramax L5P engine and Allison 1000 transmission have proven to be exceptionally durable and reliable powertrains. Well-maintained examples of the 2017-2019 Sierra 2500HD continue to command strong resale values in the used car market. The engine is known for its longevity, with many units exceeding 200,000 miles without major issues. Regular maintenance, including oil changes and fuel filter replacements, is crucial for ensuring the long-term health of the engine and transmission. This particular generation of Sierra 2500HD remains a popular choice for buyers seeking a capable and dependable heavy-duty truck.
