2017-2019 GMC Sierra 2500HD IV (GMTK2XX) Double Cab Standard Box 6.6 Duramax TD V8 (445 Hp) Automatic

The GMC Sierra 2500HD IV (GMTK2XX) Double Cab Standard 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 requiring substantial towing capacity and robust performance. It was part of the fourth generation (GMTK2XX) of the Sierra/Silverado HD series, known for its increased strength and refined features compared to its predecessors. This configuration aimed to balance power with usability, offering a step up from the gasoline engine options while remaining more accessible than the highest-output diesel trims.

Technical Specifications

Powertrain & Engine Architecture

The heart of this Sierra 2500HD variant is the Duramax L5P 6.6-liter turbocharged diesel V8. This engine represents a significant evolution of the Duramax design, incorporating technologies to improve both power and efficiency. The L5P utilizes a cast iron block and aluminum cylinder heads, a robust combination designed for longevity and high-stress applications. The engine employs a common-rail direct fuel injection system, delivering fuel at extremely high pressures for optimized combustion. A variable geometry turbocharger (VGT) and intercooler further enhance performance by increasing air intake and reducing intake air temperature. The overhead valve (OHV) valvetrain, while a traditional design, is known for its durability and simplicity. Paired with the engine is the Allison 1000 six-speed automatic transmission, renowned for its strength and smooth shifting characteristics. This transmission is specifically calibrated for the high torque output of the Duramax engine, providing confident and controlled power delivery.

Driving Characteristics

The 445 horsepower and 910 lb-ft of torque produced by the L5P Duramax engine translate into impressive real-world performance. While not as overtly quick as some gasoline-powered trucks, the 2500HD offers a commanding presence and effortless towing capability. The Allison transmission’s gear ratios are optimized for hauling, providing ample low-end torque for starting with heavy loads and maintaining speed on inclines. Compared to the 6.0-liter gasoline V8 option, the Duramax provides significantly more torque, making it the preferred choice for those regularly towing trailers or hauling heavy payloads. Compared to the higher-output Duramax variants (typically exceeding 470 hp), this 445 hp version offers a slightly more relaxed driving experience, with a focus on smooth power delivery rather than outright acceleration. The automatic transmission, while capable, doesn’t offer the same level of driver control as a manual transmission, but it simplifies operation, especially in stop-and-go traffic.

Equipment & Trim Levels

The 6.6 Duramax/Allison combination was typically offered on higher trim levels of the Sierra 2500HD, such as the SLT, and Denali. Standard features included air conditioning, power windows and locks, a rearview camera, and a basic infotainment system. The SLT trim added leather upholstery, heated front seats, and a more advanced infotainment system with navigation. The Denali trim, the most luxurious offering, included premium leather, wood trim, and a host of additional convenience features. Optional extras included a sunroof, upgraded audio system, and various driver-assistance technologies. The Double Cab configuration provided a spacious rear seat, making it suitable for both work and family use. The standard box length offered a good balance between cargo capacity and maneuverability.

Chassis & Braking

The Sierra 2500HD features a fully boxed frame, 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 configuration is designed to handle heavy loads and provide a comfortable ride. 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, with options available to optimize for towing or fuel economy. Stabilizer bars were included to reduce body roll during cornering.

Market Reception & Comparison

The GMC Sierra 2500HD with the 6.6-liter Duramax engine consistently received positive reviews from automotive critics. The engine was praised for its power, torque, and refinement. The Allison transmission was also lauded for its smooth shifting and durability. Fuel economy, while not a primary concern for heavy-duty truck buyers, was considered competitive within the segment. Compared to the gasoline engine options, the Duramax offered significantly better towing capacity and fuel efficiency when hauling heavy loads. Compared to Ford’s Super Duty and Ram’s heavy-duty trucks, the Sierra 2500HD was often seen as offering a more refined interior and a smoother ride. However, some critics noted that the GMC’s price was slightly higher than its competitors.

Legacy

The Duramax L5P engine has proven to be a remarkably reliable powertrain. With proper maintenance, these engines are known to exceed 200,000 miles without major issues. The Allison transmission is equally durable. On the used car market, Sierra 2500HDs equipped with this engine and transmission combination command a premium price due to their reputation for reliability and capability. These trucks remain popular choices for those needing a robust and dependable workhorse. The GMTK2XX platform, while superseded by newer generations, continues to be well-regarded for its strength and durability, ensuring the 2017-2019 Sierra 2500HD remains a relevant and desirable vehicle for years to come.