The GMC Sierra 2500HD III (GMT900) Crew Cab Standard Box, equipped with the 6.6-liter Duramax TD V8 engine and automatic transmission, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2007 to 2010, this variant occupied a crucial position in the American full-size pickup market, catering to buyers needing substantial towing and hauling capabilities combined with the comfort of a crew cab. It was part of the GMT900 platform generation, a substantial redesign for GMC and Chevrolet’s heavy-duty trucks, focusing on increased strength, improved refinement, and enhanced diesel powertrain options.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900) Crew Cab Standard Box |
| Type (Engine) | 6.6 Duramax TD V8 (365 Hp) Automatic |
| Start of production | 2007 |
| End of production | 2010 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8 kg/Hp, 125.4 Hp/tonne |
| Weight-to-torque ratio | 3.3 kg/Nm, 307.5 Nm/tonne |
| Power | 365 Hp @ 3200 rpm |
| Power per litre | 55.3 Hp/l |
| Torque | 895 Nm @ 1600 rpm (660.12 lb.-ft. @ 1600 rpm) |
| Maximum engine speed | 3450 rpm |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Duramax LMM |
| 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 | 16.8:1 |
| 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 | 24 l (25.36 US qt | 21.12 UK qt) |
| Kerb Weight | 2911 kg (6417.66 lbs.) |
| Max. weight | 4173 kg (9199.89 lbs.) |
| Max load | 1262 kg (2782.23 lbs.) |
| Trunk (boot) space – maximum | 1718 l (60.67 cu. ft.) |
| Permitted trailer load with brakes (12%) | 5897 kg (13000.66 lbs.) |
| Length | 6094 mm (239.92 in.) |
| Width including mirrors | 2032 mm (80 in.) |
| Height | 1958 mm (77.09 in.) |
| Wheelbase | 3886 mm (152.99 in.) |
| Front track | 1744 mm (68.66 in.) |
| Rear (Back) track | 1676 mm (65.98 in.) |
| Ride height (ground clearance) | 243 mm (9.57 in.) |
| Minimum turning circle (turning diameter) | 15.6 m (51.18 ft.) |
| Drivetrain Architecture | Rear wheel drive |
| Number of gears and type of gearbox | 6 gears, automatic transmission Allison |
| Front suspension | Independent torsion bar, double wishbone |
| Rear suspension | Rigid axle suspension, Leaf spring |
| Front brakes | Ventilated discs, 325×38 mm |
| Rear brakes | Ventilated discs, 325×30 mm |
| Tires size | 245/75 R16; 265/75 R17 |
| Wheel rims size | 6.5J x 16; 7.5J x 17 |
INTRODUCTION
The 2007-2010 GMC Sierra 2500HD Crew Cab with the 6.6L Duramax diesel and Allison automatic transmission was a workhorse designed for demanding tasks. Positioned as a heavy-duty offering within the GMC Sierra lineup, it catered to customers requiring significant towing capacity and payload. The Crew Cab configuration provided ample passenger space, making it suitable for both work and family use. This generation marked a substantial improvement over its predecessor, with a fully boxed frame, enhanced suspension geometry, and a more refined interior. The Duramax engine, paired exclusively with the Allison transmission in this configuration, became a benchmark for diesel performance and durability in the heavy-duty truck segment.
Powertrain & Engine Architecture
At the heart of this Sierra 2500HD lies the Duramax LMM 6.6-liter V8 diesel engine. This engine represented a significant evolution of the previous LBZ Duramax, incorporating a revised combustion chamber, improved fuel injectors, and a more robust cooling system. The LMM utilized a common-rail fuel injection system, delivering fuel at extremely high pressures for optimized combustion efficiency and reduced emissions. The engine featured an overhead valve (OHV) valvetrain, known for its simplicity and reliability. A variable geometry turbocharger and intercooler further enhanced performance and reduced turbo lag. The Allison 1000 six-speed automatic transmission was specifically designed to handle the high torque output of the Duramax engine. This transmission featured a lock-up torque converter for improved fuel efficiency and a heavy-duty cooling system to prevent overheating under strenuous conditions. The transmission’s gear ratios were optimized for both towing and everyday driving, providing a balance of power and efficiency.
Driving Characteristics
The 6.6L Duramax/Allison combination in the Sierra 2500HD delivered a robust and capable driving experience. While not designed for outright speed, the engine produced a substantial 895 lb-ft of torque, making it exceptionally adept at towing heavy loads. Acceleration was brisk, especially considering the truck’s weight, and the Allison transmission shifted smoothly and decisively. Compared to the gasoline-powered Sierra 2500HD models, the diesel offered significantly more low-end torque, making it easier to pull heavy trailers up steep grades. The automatic transmission, while convenient, did result in a slight performance deficit compared to the available manual transmission, as some power was lost through the torque converter. However, the Allison’s six gears helped to keep the engine in its optimal power band, maximizing efficiency and minimizing engine strain. The ride quality, while firm due to the heavy-duty suspension, was reasonably comfortable for a truck of this size.
Equipment & Trim Levels
The Sierra 2500HD Crew Cab with the Duramax engine typically came well-equipped, though specific features varied depending on the trim level. Standard features generally included air conditioning, power windows and locks, a CD player, and cloth upholstery. Higher trim levels, such as the SLT and Denali, added features like leather upholstery, heated seats, a premium sound system, navigation, and a sunroof. Optional extras included a trailer brake controller, a backup camera, and various appearance packages. The Crew Cab configuration offered generous interior space, with seating for five adults. The standard box provided a practical cargo bed length for hauling various materials.
Chassis & Braking
The GMT900 platform featured a fully boxed frame, significantly increasing its strength and rigidity compared to previous generations. The front suspension utilized an independent torsion bar setup with double wishbone control arms, providing a comfortable ride and precise handling. The rear suspension employed a traditional leaf spring design, optimized for heavy-duty hauling. Braking duties were handled by ventilated disc brakes on all four wheels, providing ample stopping power even when towing heavy loads. An Anti-lock Braking System (ABS) was standard. The truck’s robust chassis and braking system were designed to handle the substantial weight and torque output of the Duramax engine.
Market Reception & Comparison
The 2007-2010 GMC Sierra 2500HD with the Duramax diesel and Allison automatic received generally positive reviews from automotive critics. It was praised for its powerful engine, smooth transmission, and comfortable ride. Compared to the gasoline-powered Sierra 2500HD models, the diesel offered superior towing capacity and fuel economy, especially when hauling heavy loads. However, the diesel engine carried a significant price premium. Compared to competitors like the Ford Super Duty and Ram 2500, the Sierra 2500HD was often considered to be a well-rounded offering, with a good balance of performance, comfort, and reliability. Fuel economy, while better than gasoline counterparts, was still relatively low, averaging around 14-17 mpg in real-world driving.
Legacy
The Duramax LMM engine and Allison transmission pairing in the 2007-2010 GMC Sierra 2500HD has proven to be remarkably durable and reliable. These trucks continue to be highly sought after in the used car market, particularly by those needing a capable and dependable work truck. While some maintenance items, such as the fuel injectors and turbocharger, may require attention after high mileage, the engine is generally considered to be one of the most robust diesel engines ever produced. The Allison transmission is also known for its longevity and ability to withstand abuse. The GMT900 generation Sierra 2500HD established a strong reputation for its heavy-duty capabilities and remains a popular choice for owners who demand a powerful and reliable truck.
