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 an Allison automatic transmission, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2015 to 2017, this configuration occupied a sweet spot in the Sierra 2500HD lineup, offering a balance of robust towing capacity, comfortable interior space, and refined diesel performance. It was positioned as a workhorse for those needing substantial capability without necessarily opting for the highest trim levels or the most extreme performance options.
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) 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 | 8.1 kg/Hp, 123.2 Hp/tonne |
| Weight-to-torque ratio | 3.1 kg/Nm, 321.8 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 | 3222 kg (7103.29 lbs.) |
| Max. weight | 4536 kg (10000.17 lbs.) |
| Max load | 1314 kg (2896.87 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 | 1988 mm (78.27 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) | 213 mm (8.39 in.) |
| Minimum turning circle (turning diameter) | 15.7 m (51.51 ft.) |
| Drivetrain Architecture | Rear wheel drive |
| 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 |
| 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
At the heart of this Sierra 2500HD variant lies the Duramax LML 6.6-liter turbocharged diesel V8. This engine, a cornerstone of GMC’s heavy-duty offerings, is renowned for its durability and substantial torque output. The LML iteration introduced several refinements over its predecessor, including a redesigned combustion chamber, improved fuel injectors, and a more efficient turbocharger. These changes contributed to increased horsepower and torque while also reducing emissions. The engine utilizes a diesel commonrail fuel injection system, delivering highly pressurized fuel directly into the cylinders for optimal combustion. The overhead valve (OHV) valvetrain, while a more traditional design, proved reliable and well-suited to the demands of heavy-duty trucking. The Allison 1000 six-speed automatic transmission is a critical component, specifically engineered to handle the immense torque produced by the Duramax engine. Known for its robustness and smooth shifting, the Allison transmission played a key role in maximizing the truck’s towing and hauling capabilities.
Driving Characteristics
The 6.6-liter Duramax with the Allison automatic provided a distinctly different driving experience compared to gasoline-powered Sierra 2500HDs or even those equipped with the smaller 6.0-liter gasoline V8. The diesel engine’s peak torque, available at a relatively low 1600 rpm, meant that the truck could effortlessly pull heavy loads without requiring frequent downshifts. The Allison transmission’s programming was optimized for towing, prioritizing smooth, confident shifts over outright acceleration. While not a sports truck by any means, the 397 horsepower provided adequate power for highway cruising and merging. Compared to the manual transmission options, the automatic offered greater convenience, particularly in stop-and-go traffic or when navigating challenging terrain. However, some drivers preferred the more direct control offered by a manual gearbox. The gear ratios in the Allison transmission were carefully selected to balance fuel efficiency and towing performance.
Equipment & Trim Levels
The 2500HD Crew Cab Standard Box with the Duramax/Allison combination was typically offered in SLE and SLT trim levels. The SLE trim provided a good level of standard equipment, including air conditioning, power windows and locks, a basic audio system, and cloth upholstery. The SLT trim added features such as leather upholstery, heated front seats, a premium audio system, and additional chrome exterior trim. Optional extras included a navigation system, a rear-seat entertainment system, and various towing packages. The Crew Cab configuration offered spacious seating for five passengers, making it a practical choice for families or work crews.
Chassis & Braking
The Sierra 2500HD’s chassis was designed to withstand the stresses of heavy-duty use. The front suspension featured coil springs and a double wishbone design, while the rear suspension utilized a traditional leaf spring setup. A transverse stabilizer bar helped to reduce body roll during cornering. Braking duties were handled by ventilated disc brakes at all four corners, providing ample stopping power even when towing heavy loads. An Anti-lock Braking System (ABS) was standard equipment. The truck’s robust frame and heavy-duty suspension components contributed to its impressive towing and payload capacities.
Market Reception & Comparison
The GMC Sierra 2500HD with the 6.6-liter Duramax and Allison automatic was generally well-received by critics and consumers alike. It was praised for its powerful engine, smooth transmission, and comfortable ride. Fuel economy, while not exceptional, was respectable for a heavy-duty truck. Compared to the gasoline-powered Sierra 2500HDs, the Duramax diesel offered significantly better fuel economy and towing performance. However, the diesel engine carried a higher price tag and required more frequent maintenance, such as diesel exhaust fluid (DEF) refills and particulate filter servicing. Compared to competitors like the Ford Super Duty and Ram 2500, the Sierra 2500HD was often seen as a more refined and comfortable option, although some competitors offered slightly higher towing capacities.
Legacy
The Duramax LML engine and Allison transmission pairing in the 2015-2017 GMC Sierra 2500HD has proven to be remarkably reliable. These trucks continue to be sought after on the used car market, particularly by those needing a capable and dependable work truck. Properly maintained examples can easily exceed 200,000 miles without major mechanical issues. The Duramax engine’s longevity and the Allison transmission’s robustness have cemented their reputations as industry benchmarks for heavy-duty powertrain reliability. While newer Sierra 2500HD models offer even more power and technology, the 2015-2017 generation remains a compelling option for buyers seeking a proven and capable heavy-duty truck at a reasonable price.
