The GMC Sierra 2500HD IV (GMTK2XX) Crew Cab Standard Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 397 horsepower and paired with a 6-speed Allison automatic transmission and four-wheel drive, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2015 to 2017, this variant occupied a premium position within the Sierra 2500HD lineup, targeting buyers needing substantial towing and hauling capacity without sacrificing comfort or refinement. It was part of the fourth generation of the Sierra HD series, known as the GMTK2XX platform, which brought substantial improvements in capability, interior space, and technology compared to its predecessors.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD IV (GMTK2XX) Crew Cab Standard Box |
| Type (Engine) | 6.6 Duramax TD V8 (397 Hp) 4WD Automatic |
| Start of production | 2015 |
| End of production | 2017 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 7.5 kg/Hp, 134 Hp/tonne |
| Weight-to-torque ratio | 2.9 kg/Nm, 350 Nm/tonne |
| Power | 397 Hp @ 3000 rpm |
| Power per litre | 60.2 Hp/l |
| Torque | 1037 Nm @ 1600 rpm, 764.85 lb.-ft. @ 1600 rpm |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Duramax LML |
| Engine displacement | 6599 cm3, 402.7 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 | 22.4 l, 23.67 US qt | 19.71 UK qt |
| Kerb Weight | 2963 kg, 6532.3 lbs. |
| Max. weight | 4309 kg, 9499.72 lbs. |
| Max load | 1346 kg, 2967.42 lbs. |
| Trunk (boot) space – maximum | 1728 l, 61.02 cu. ft. |
| Fuel tank capacity | 136 l, 35.93 US gal | 29.92 UK gal |
| Permitted trailer load with brakes (12%) | 5897 kg, 13000.66 lbs. |
| Length | 6083 mm, 239.49 in. |
| Width including mirrors | 2045 mm, 80.51 in. |
| Height | 1987 mm, 78.23 in. |
| Wheelbase | 3904 mm, 153.7 in. |
| Front track | 1748 mm, 68.82 in. |
| Rear (Back) track | 1709 mm, 67.28 in. |
| Ride height (ground clearance) | 208 mm, 8.19 in. |
| Minimum turning circle (turning diameter) | 15.7 m, 51.51 ft. |
| Drivetrain Architecture | All wheel drive (4×4). ICE drives rear wheels, front wheels engaged via clutch. |
| 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 LML 6.6-liter turbocharged diesel V8. This engine represents a refinement of the previous LBZ and LMM Duramax engines, incorporating a redesigned combustion chamber, improved fuel injection system, and a more efficient turbocharger. The LML utilizes a common-rail direct injection system, delivering fuel at extremely high pressures for optimized combustion and reduced emissions. The engine features an overhead valve (OHV) valvetrain, a design choice favored for its durability and low-end torque characteristics. The Allison 1000 six-speed automatic transmission is specifically calibrated for the high torque output of the Duramax engine. This transmission is renowned for its robustness and smooth shifting, crucial for heavy-duty applications. The transmission features a lock-up torque converter to improve fuel efficiency at highway speeds.
Driving Characteristics
The 397 horsepower and 765 lb-ft of torque delivered by the LML Duramax engine, coupled with the Allison automatic, provides a commanding driving experience. While not as overtly quick as gasoline-powered trucks, the Sierra 2500HD excels in situations demanding substantial pulling power. The automatic transmission is programmed for smooth, deliberate shifts, prioritizing stability and control when towing. Compared to the 6.0L gasoline V8 option, the Duramax offers significantly more low-end torque, making it far more capable for heavy hauling. The 6-speed Allison transmission’s gear ratios are optimized for both towing and highway cruising, providing adequate acceleration in most situations. Compared to manual transmission equipped Duramax models, the automatic offers a more relaxed driving experience, particularly in stop-and-go traffic, but may sacrifice some driver control and fuel efficiency.
Equipment & Trim Levels
The Crew Cab Standard Box configuration offered a spacious interior with seating for five passengers. Standard features typically included air conditioning, power windows and locks, a basic audio system, and vinyl upholstery. Higher trim levels, such as the SLT and Denali, added features like leather upholstery, heated and ventilated front seats, a premium audio system, navigation, and advanced safety technologies. Optional extras included a sunroof, rear-seat entertainment system, and various towing packages. The Standard Box length provided a good balance between cargo capacity and maneuverability.
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 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 rear axle ratios varied depending on the specific configuration, influencing both towing capacity and fuel economy.
Market Reception & Comparison
The 2015-2017 GMC Sierra 2500HD with the Duramax diesel and Allison automatic was generally well-received by critics and consumers alike. It was praised for its robust powertrain, comfortable ride, and spacious interior. Fuel economy, while not exceptional, was competitive for a heavy-duty truck. Compared to the Ford Super Duty and Ram 2500/3500, the Sierra 2500HD offered a compelling combination of capability, refinement, and value. The Duramax engine was consistently ranked among the best diesel engines in the heavy-duty truck segment.
Legacy
The Duramax LML engine paired with the Allison transmission has proven to be a durable and reliable powertrain. Properly maintained, these engines can easily exceed 200,000 miles. On the used car market, these Sierra 2500HD models hold their value relatively well, particularly those with lower mileage and well-documented maintenance histories. The GMTK2XX platform is considered a significant step forward in heavy-duty truck design, offering a blend of capability, comfort, and technology that continues to appeal to buyers today. The LML Duramax remains a sought-after engine for those needing a powerful and dependable diesel powertrain.
