2007-2010 GMC Sierra 3500HD III (GMT900) Regular Cab Long Box 6.6 Duramax TD V8 (365 Hp) 4WD SRW Automatic

The GMC Sierra 3500HD III, produced between 2007 and 2010, represented a significant evolution in GMC’s heavy-duty truck lineup. Part of the GMT900 generation, this iteration of the Sierra 3500HD was offered in various configurations, including a Regular Cab with a Long Box, and was particularly notable for its available 6.6-liter Duramax turbodiesel V8 engine paired with a four-speed Allison automatic transmission. This combination targeted buyers needing substantial towing and hauling capacity, positioning it as a workhorse within the GMC truck family. The Regular Cab/Long Box configuration was aimed at customers prioritizing cargo space and utility over passenger comfort, making it popular with tradesmen, farmers, and those frequently towing large trailers.

Technical Specifications

Powertrain & Engine Architecture

The heart of this Sierra 3500HD variant is the Duramax LMM 6.6-liter V8 diesel engine. This engine, a product of Isuzu and General Motors collaboration, represented a refinement of the previous LBZ Duramax. The LMM featured a redesigned combustion chamber and improved fuel injection system, contributing to increased power and reduced emissions. The engine utilizes a common-rail direct injection system, delivering fuel at extremely high pressures for optimized combustion. The valvetrain employs an overhead valve (OHV) configuration, known for its simplicity and durability. A variable geometry turbocharger and intercooler further enhance performance by providing increased air intake. The engine’s robust construction and advanced technologies allowed it to produce 365 horsepower at 3200 rpm and a substantial 895 lb-ft of torque at 1600 rpm. This power is channeled through a heavy-duty six-speed Allison automatic transmission, specifically designed to handle the engine’s high torque output and the demands of heavy hauling. The Allison transmission featured a lock-up torque converter for improved fuel efficiency at highway speeds.

Driving Characteristics

The 6.6L Duramax with the Allison automatic in the Sierra 3500HD delivered a driving experience focused on capability rather than outright speed. The substantial torque available from low engine speeds made it exceptionally adept at towing and hauling heavy loads. While not as quick as gasoline-powered counterparts, the diesel engine provided a strong and consistent pull, even when fully loaded. The Allison transmission shifted smoothly and predictably, contributing to a comfortable driving experience. Compared to the 6.0L gasoline V8 offered in the same generation, the Duramax provided significantly more torque and towing capacity, albeit with a higher initial cost. The automatic transmission, while convenient, didn’t offer the same level of control as a manual transmission, particularly when descending steep grades with a heavy load. However, the Allison’s integrated tow/haul mode adjusted shift points to optimize performance and engine braking.

Equipment & Trim Levels

The Sierra 3500HD in this configuration typically came standard with features geared towards work and utility. This included a heavy-duty suspension, locking rear differential, and a robust frame. Interior appointments were functional and durable, with vinyl or cloth upholstery being common. Standard features often included air conditioning, an AM/FM radio, and basic instrumentation. Optional extras could include power windows and locks, a premium audio system, and upgraded interior trim. The Regular Cab configuration prioritized interior space for tools and equipment over passenger comfort. Trim levels varied, but generally offered incremental upgrades in interior features and exterior styling.

Chassis & Braking

The Sierra 3500HD’s chassis was designed for heavy-duty use. It featured a fully boxed frame constructed from high-strength steel. The front suspension utilized an independent torsion bar setup with double wishbones, providing a comfortable ride and good handling. The rear suspension employed a traditional leaf spring design, optimized for load-carrying capacity. Braking duties were handled by ventilated disc brakes on all four wheels, providing ample stopping power even with heavy loads. An Anti-lock Braking System (ABS) was standard, enhancing safety and control. The rear axle was typically a single rear wheel (SRW) configuration, although dual rear wheel (DRW) options were available for even greater towing capacity.

Market Reception & Comparison

The 6.6L Duramax-equipped Sierra 3500HD was generally well-received by critics and consumers alike. It was praised for its exceptional towing and hauling capabilities, as well as its relatively smooth and quiet operation for a diesel engine. Fuel economy was a strong point, particularly when compared to gasoline-powered alternatives. However, the higher initial cost of the Duramax engine and the complexity of its emissions control systems were noted as potential drawbacks. Compared to the Ford Super Duty and Ram Heavy Duty trucks of the same era, the Sierra 3500HD offered a competitive combination of power, capability, and refinement.

Legacy

The GMT900-generation Sierra 3500HD, particularly the 6.6L Duramax/Allison automatic combination, has proven to be a durable and reliable truck. These trucks remain popular in the used market, often commanding premium prices due to their reputation for longevity and capability. The LMM Duramax engine, while subject to some emissions-related issues, is generally considered a robust and dependable powerplant. Regular maintenance, including timely oil changes and fuel filter replacements, is crucial for ensuring long-term reliability. Today, these trucks continue to serve as workhorses for many owners, demonstrating the enduring quality and capability of the GMC Sierra 3500HD.