The GMC Sierra 2500HD IV (GMTK2XX) Crew Cab Long Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 445 horsepower and paired with a 6-speed Allison automatic transmission, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2017 to 2019, this configuration occupied a premium position within the Sierra 2500HD lineup, targeting buyers requiring substantial towing capacity and robust performance for work or recreational purposes. It built upon the foundation of the GMTK2XX platform, offering enhanced capability and refinement compared to its predecessors.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD IV (GMTK2XX) Crew 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 | 7.8 kg/Hp, 128.8 Hp/tonne |
| Weight-to-torque ratio | 2.8 kg/Nm, 357.1 Nm/tonne |
| Power | 445 Hp @ 2800 rpm |
| Power per litre | 67.5 Hp/l |
| Torque | 1234 Nm @ 1600 rpm (910.15 lb.-ft. @ 1600 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Duramax L5P |
| Engine displacement | 6588 cm3 (402.02 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 | 3456 kg (7619.18 lbs.) |
| Max. weight | 4536 kg (10000.17 lbs.) |
| Max load | 1080 kg (2380.99 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 | 6563 mm (258.39 in.) |
| Width including mirrors | 2045 mm (80.51 in.) |
| Height | 1980 mm (77.95 in.) |
| Wheelbase | 4258 mm (167.64 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Minimum turning circle (turning diameter) | 17.1 m (56.1 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 | 235/80 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 a cast iron block, aluminum cylinder heads, and a robust rotating assembly. The L5P utilizes a common-rail direct fuel injection system, delivering fuel at extremely high pressures for optimized combustion. A variable geometry turbocharger (VGT) and intercooler work in tandem to maximize power and efficiency. The engine’s overhead valve (OHV) valvetrain, while traditional, is known for its durability and simplicity. The Allison 1000 6-speed automatic transmission is specifically designed to handle the high torque output of the Duramax engine. This transmission features a lock-up torque converter for improved fuel economy and a heavy-duty cooling system to prevent overheating under demanding conditions.
Driving Characteristics
The 445 horsepower and 910 lb-ft of torque delivered by this powertrain configuration provide exceptional towing and hauling capabilities. While not designed for outright speed, the Sierra 2500HD offers strong acceleration, particularly when unloaded. The Allison transmission is well-tuned for smooth and confident shifts, although it may exhibit some hunting for the optimal gear in certain situations. Compared to the gasoline-powered versions of the Sierra 2500HD, the Duramax diesel provides significantly more low-end torque, making it ideal for towing heavy loads. Compared to other Duramax configurations, like those with slightly less power, this variant offered a noticeable performance increase, making it a popular choice for those needing maximum capability.
Equipment & Trim Levels
The Crew Cab Long Box configuration, combined with the Duramax engine, typically came in higher trim levels such as SLE, SLT, and Denali. Standard features generally included air conditioning, power windows and locks, a rearview camera, and a basic infotainment system. Higher trims added features like leather upholstery, heated and ventilated front 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 comfortable seating and a user-friendly layout.
Chassis & Braking
The Sierra 2500HD features a fully boxed frame designed for strength and rigidity. The front suspension utilizes coil springs and a double wishbone setup, while the rear suspension employs leaf springs. This configuration provides a comfortable ride while maintaining excellent load-carrying capacity. Braking duties are handled by ventilated disc brakes on all four wheels, providing ample stopping power even when towing heavy loads. An Anti-lock Braking System (ABS) is standard. The rear axle ratios varied depending on the specific configuration, influencing both towing capacity and fuel economy.
Market Reception & Comparison
The 6.6-liter Duramax diesel engine consistently received positive reviews for its power, reliability, and fuel efficiency. Critics praised the Sierra 2500HD’s towing capabilities and overall refinement. Compared to the gasoline-powered Sierra 2500HD, the diesel version offered significantly better fuel economy when towing, making it a cost-effective choice for frequent haulers. Compared to competing heavy-duty trucks from Ford and Ram, the Sierra 2500HD was often seen as a strong contender, offering a compelling combination of performance, features, and value.
Legacy
The Duramax L5P engine has proven to be exceptionally durable, with many examples exceeding 200,000 miles with proper maintenance. The Allison transmission is also known for its longevity and reliability. On the used car market, Sierra 2500HDs equipped with this powertrain configuration command a premium price due to their proven capabilities and reputation for dependability. Regular maintenance, including oil changes and fuel filter replacements, is crucial for ensuring the long-term health of this powertrain. The GMTK2XX platform Sierra 2500HD remains a popular choice for those seeking a capable and reliable heavy-duty truck.
