The GMC Sierra 3500HD IV (GMTK2XX) Crew Cab Long Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 397 horsepower and paired with a 4WD SRW Automatic transmission, 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 3500HD lineup, targeting buyers requiring substantial towing and hauling capabilities combined with a degree of comfort and refinement. It was part of the fourth generation of the Sierra/Silverado HD trucks, known as the GMTK2XX platform, which brought substantial improvements in capability, interior space, and technology.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD IV (GMTK2XX) Crew Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (397 Hp) 4WD SRW 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 | 8.8 kg/Hp, 114.2 Hp/tonne |
| Weight-to-torque ratio | 3.4 kg/Nm, 298.4 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 | 29.7 l (31.38 US qt | 26.13 UK qt) |
| Kerb Weight | 3475 kg (7661.06 lbs.) |
| Max. weight | 5262 kg (11600.72 lbs.) |
| Max load | 1787 kg (3939.66 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%) | 6804 kg (15000.25 lbs.) |
| Length | 6563 mm (258.39 in.) |
| Width including mirrors | 2045 mm (80.51 in.) |
| Height | 1983 mm (78.07 in.) |
| Wheelbase | 4259 mm (167.68 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Ride height (ground clearance) | 218 mm (8.58 in.) |
| Minimum turning circle (turning diameter) | 17.1 m (56.1 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, Wishbone |
| Rear suspension | Rigid axle suspension, Leaf spring |
| Front brakes | Ventilated discs, 355×40 mm |
| Rear brakes | Ventilated discs, 373×34 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| Tires size | 235/80 R17; 265/70 R18 |
| Wheel rims size | 7.5J x 17; 8J x 18 |
Powertrain & Engine Architecture
The heart of this Sierra 3500HD 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 injectors, and a more efficient turbocharger. The LML utilizes a common-rail direct fuel injection system, delivering fuel at extremely high pressures for optimized combustion. The engine features an overhead valve (OHV) valvetrain, a design choice favored for its durability and low-end torque characteristics. The turbocharger and intercooler work in tandem to increase air density, boosting power and efficiency. The Allison 1000 six-speed automatic transmission is specifically tuned to handle the immense torque output of the Duramax engine. This transmission is known for its robustness and smooth shifting, crucial for heavy-duty applications.
Driving Characteristics
The 397 horsepower and 764.85 lb-ft of torque delivered by this powertrain configuration translate into impressive real-world performance. While not as overtly quick as lighter-duty trucks or those equipped with gasoline engines, the Sierra 3500HD with the Duramax and Allison transmission excels at towing and hauling. The Allison transmission’s gear ratios are optimized for maximizing torque at lower RPMs, providing strong acceleration even when heavily loaded. Compared to the 6.0L gasoline V8 option, the Duramax offers significantly more torque and better fuel economy, especially under load. The automatic transmission, while convenient, doesn’t offer the same level of control as a manual transmission, but it simplifies operation for drivers spending long hours behind the wheel.
Equipment & Trim Levels
The Crew Cab Long Box configuration, combined with the Duramax engine, typically placed this Sierra 3500HD in the higher trim levels, such as LTZ or Denali. Standard features included air conditioning, power windows and locks, a premium audio system, and a rearview camera. LTZ trims added leather upholstery, heated and ventilated front seats, and a navigation system. The Denali trim, the most luxurious option, featured unique exterior styling, upgraded interior materials, and additional convenience features. Optional extras included a sunroof, a rear-seat entertainment system, and various towing packages.
Chassis & Braking
The Sierra 3500HD’s chassis is built for durability and heavy-duty use. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs a traditional leaf spring setup. This configuration provides a comfortable ride while maintaining a high payload 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 was typically a single rear wheel (SRW) configuration, though dual rear wheel (DRW) options were available for even greater towing capacity.
Market Reception & Comparison
The 2015-2017 GMC Sierra 3500HD with the Duramax diesel and Allison automatic received generally positive reviews. Critics praised its powerful engine, smooth transmission, and comfortable ride. Fuel economy, while not exceptional, was considered good for a heavy-duty truck of its size and capability. Compared to the Ford Super Duty and Ram 3500, the Sierra 3500HD was often seen as offering a more refined interior and a quieter cabin. However, some reviewers noted that the GMC’s price was higher than its competitors. The Duramax engine’s reliability was generally considered excellent, though maintenance costs were higher than those associated with gasoline engines.
Legacy
The Duramax LML engine paired with the Allison transmission has proven to be a remarkably durable and reliable powertrain. Well-maintained examples of the 2015-2017 Sierra 3500HD continue to command strong resale values in the used car market. The engine is known for its longevity, with many examples exceeding 200,000 miles with proper care. The GMTK2XX platform represented a significant step forward for GMC’s heavy-duty trucks, establishing a benchmark for capability, comfort, and technology in the segment. This particular configuration remains a popular choice for buyers seeking a powerful and dependable truck for demanding work or recreational towing needs.
