The GMC Sierra 2500HD IV (GMTK2XX) Double Cab Long Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 445 horsepower, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2017 to 2019, 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 (GMTK2XX) of the Sierra/Silverado HD platform, known for its increased strength and capability compared to its predecessors.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD IV (GMTK2XX) Double Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) Automatic |
| Start of production | 2017 year |
| End of production | 2019 year |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 6.3 kg/Hp, 158.3 Hp/tonne |
| Weight-to-torque ratio | 2.3 kg/Nm, 438.8 Nm/tonne |
| Power | 445 Hp @ 2800 rpm |
| Power per litre | 67.4 Hp/l |
| Torque | 1234 Nm @ 1600 rpm (910.15 lb.-ft. @ 1600 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Duramax L5P |
| Engine displacement | 6604 cm3 (403 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 | 2812 kg (6199.4 lbs.) |
| Max. weight | 4309 kg (9499.72 lbs.) |
| Max load | 1497 kg (3300.32 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 | 6322 mm (248.9 in.) |
| Width including mirrors | 2045 mm (80.51 in.) |
| Height | 1978 mm (77.87 in.) |
| Wheelbase | 4017 mm (158.15 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Minimum turning circle (turning diameter) | 16.2 m (53.15 ft.) |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels of the vehicle. |
| Drive wheel | 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 |
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, featuring 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. The turbocharger, coupled with an intercooler, provides increased air density for enhanced power output. The engine employs an overhead valve (OHV) valvetrain, a design choice prioritizing durability and low-end torque. The Allison 1000 six-speed automatic transmission is paired with the Duramax, specifically tuned to handle the engine’s substantial torque output. This transmission is known for its durability and smooth shifting characteristics, crucial for heavy-duty applications.
Driving Characteristics
The 445 horsepower and 910 lb-ft of torque delivered by the Duramax engine and Allison transmission combination provide impressive performance. While not designed for outright speed, this configuration excels in towing and hauling. Acceleration is brisk, even with a substantial load. The Allison transmission’s programming prioritizes smooth, confident shifts, making it easy to manage power delivery. Compared to the 6.0L gasoline V8 option, the Duramax offers significantly more torque at lower RPMs, making it ideal for demanding tasks. Compared to the 2500HD models equipped with the 6.6L gasoline engine, the diesel variant provides a much more relaxed driving experience when towing, with less need for frequent downshifts. The automatic transmission, while convenient, doesn’t offer the same level of control as a manual transmission, but it compensates with ease of use and reduced driver fatigue.
Equipment & Trim Levels
The Double Cab Long Box configuration offered a spacious interior with seating for five passengers. Standard features typically included air conditioning, power windows and locks, a basic infotainment system with a touchscreen display, and a rearview camera. Higher trim levels, such as the SLT and Denali, 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 Double Cab configuration provided a good balance between passenger space and cargo bed length, making it a versatile choice for both work and family use.
Chassis & Braking
The GMTK2XX platform features a fully boxed frame constructed from high-strength steel, providing a solid foundation for heavy-duty use. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs leaf springs. This setup is tuned for a comfortable ride while maintaining excellent load-carrying capacity. Braking duties are handled by ventilated disc brakes on all four wheels. An Anti-lock Braking System (ABS) is standard. The rear axle ratios were typically chosen to optimize towing performance and fuel economy, with options available depending on the specific configuration.
Market Reception & Comparison
The 6.6-liter Duramax diesel engine consistently received positive reviews for its power, torque, and reliability. Critics praised the Allison transmission for its smooth operation and durability. The Sierra 2500HD, in general, was well-regarded for its robust construction and towing capabilities. Compared to competitors like the Ford Super Duty and Ram 2500, the Sierra 2500HD offered a competitive combination of features, performance, and value. Fuel economy, while not a primary concern for heavy-duty truck buyers, was generally considered acceptable for a vehicle of this size and capability. The Duramax/Allison combination typically commanded a higher price than gasoline-powered models, but the increased performance and towing capacity justified the cost for many buyers.
Legacy
The Duramax L5P engine has proven to be a remarkably durable and reliable powertrain. Properly maintained, these engines can easily exceed 200,000 miles. On the used car market, Sierra 2500HD models equipped with the 6.6-liter Duramax diesel and Allison automatic transmission hold their value well, reflecting their reputation for longevity and capability. Common maintenance items include regular oil changes, fuel filter replacements, and coolant flushes. The GMTK2XX platform is also considered to be relatively reliable, although potential buyers should be aware of potential issues with the emissions control system. Overall, the 2017-2019 GMC Sierra 2500HD with the 6.6L Duramax remains a highly sought-after truck for those needing a powerful and dependable workhorse.
