The GMC Sierra 3500HD IV (GMTK2XX) Regular Cab Long Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 397 horsepower and paired with a 6-speed Allison automatic transmission, represents a significant offering in the heavy-duty pickup truck segment. Produced from 2015 to 2017, this configuration was aimed at buyers needing substantial towing and hauling capacity, particularly in the commercial and agricultural sectors. It sat within the fourth generation of the Sierra 3500HD line, built on the GMTK2XX platform, which brought improvements in ride quality, interior refinement, and technology compared to its predecessors.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD IV (GMTK2XX) Regular 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 | 2 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8 kg/Hp, 124.3 Hp/tonne |
| Weight-to-torque ratio | 3.1 kg/Nm, 324.8 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 | 3193 kg (7039.36 lbs.) |
| Max. weight | 5171 kg (11400.1 lbs.) |
| Max load | 1978 kg (4360.74 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 | 5699 mm (224.37 in.) |
| Width including mirrors | 2035 mm (80.12 in.) |
| Height | 1979 mm (77.91 in.) |
| Wheelbase | 3393 mm (133.58 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Ride height (ground clearance) | 220 mm (8.66 in.) |
| Minimum turning circle (turning diameter) | 14 m (45.93 ft.) |
| Drivetrain Architecture | All wheel drive (4×4). Internal Combustion engine. |
| Number of gears and type of gearbox | 6 gears, automatic transmission Allison |
Powertrain & Engine Architecture
The heart of this Sierra 3500HD is the Duramax LML 6.6-liter turbocharged diesel V8. This engine is a testament to GMC’s commitment to heavy-duty performance. The LML represents an evolution of the Duramax design, incorporating a redesigned turbocharger, improved fuel injection system, and enhanced cooling. The engine utilizes a common-rail direct injection system, delivering fuel at extremely high pressures for optimized combustion. The overhead valve (OHV) configuration, while seemingly dated, contributes to the engine’s durability and low-end torque characteristics. The Allison 6-speed automatic transmission is renowned for its robustness and ability to handle the immense torque output of the Duramax engine. It features electronically controlled shifts and a lock-up torque converter for improved fuel efficiency.
Driving Characteristics
The combination of the 397 hp Duramax and the Allison automatic results in a truck that feels incredibly capable. While not as quick off the line as gasoline-powered alternatives, the Sierra 3500HD delivers a massive surge of torque from as low as 1600 rpm. This makes it exceptionally well-suited for towing heavy loads and navigating challenging terrain. The automatic transmission is programmed for smooth, deliberate shifts, prioritizing stability and control over outright speed. Compared to the 6.0L gasoline V8 option, the Duramax offers significantly more torque and better fuel economy, especially when towing. The 6-speed Allison transmission provides a wider range of gear ratios than older 4-speed automatics, improving both acceleration and highway cruising efficiency.
Equipment & Trim Levels
The Regular Cab Long Box configuration typically represented a work-focused trim level. Standard features included air conditioning, a basic audio system, vinyl upholstery, and manual windows and locks. However, options were available to enhance comfort and convenience, such as power windows and locks, a premium audio system, and upgraded interior trim. The Sierra 3500HD offered various trim packages, like SLE and SLT, which added features like leather upholstery, heated seats, and advanced infotainment systems. This particular configuration, being a base or work truck, often prioritized functionality over luxury.
Chassis & Braking
The Sierra 3500HD’s chassis is built for durability and heavy-duty use. It features a fully boxed frame constructed from high-strength steel. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs leaf springs. This setup provides a comfortable ride, even when the truck is heavily loaded. Braking duties are handled by ventilated discs at all four corners, providing ample stopping power. An Anti-lock Braking System (ABS) is standard. The rear axle is a solid axle, typical for heavy-duty trucks, and is designed to withstand significant loads.
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 impressive towing capacity. Fuel economy was considered good for a truck of its size and capability, averaging around 17-20 mpg on the highway. Compared to the Ford Super Duty and Ram 3500, the Sierra 3500HD was often seen as offering a more refined ride and a quieter cabin. However, some reviewers noted that the interior design was somewhat conservative compared to its competitors.
Legacy
The Duramax LML engine paired with the Allison transmission has proven to be a remarkably reliable powertrain. Properly maintained, these engines can easily exceed 200,000 miles. On the used car market, these Sierra 3500HDs hold their value well, particularly those with lower mileage and a documented maintenance history. The combination of power, durability, and towing capacity makes them a popular choice for buyers seeking a capable and long-lasting heavy-duty truck. While newer models offer more advanced technology and features, the 2015-2017 Sierra 3500HD remains a solid and dependable workhorse.
