The GMC Sierra 2500HD III, produced from 2007 to 2010, represented a significant evolution in GMC’s heavy-duty truck lineup. This generation, designated GMT900, offered a robust platform for demanding tasks, and the configuration featuring the 6.6-liter Duramax turbodiesel V8 paired with an Allison automatic transmission was a particularly popular choice for owners needing substantial towing and hauling capability. This variant occupied a sweet spot in the lineup, offering a balance between power, refinement, and usability, appealing to both commercial users and private owners. The Regular Cab Long Box configuration further emphasized its work-oriented nature, providing a spacious bed for larger loads.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900) Regular Cab Long 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 | 2 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 7.5 kg/Hp, 134.2 Hp/tonne |
| Weight-to-torque ratio | 3 kg/Nm, 329 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 | 2720 kg (5996.57 lbs.) |
| Max. weight | 4173 kg (9199.89 lbs.) |
| Max load | 1453 kg (3203.32 lbs.) |
| Trunk (boot) space – maximum | 2138 l (75.5 cu. ft.) |
| Fuel tank capacity | 129 l (34.08 US gal | 28.38 UK gal) |
| Permitted trailer load with brakes (12%) | 5897 kg (13000.66 lbs.) |
| Length | 5708 mm (224.72 in.) |
| Width including mirrors | 2032 mm (80 in.) |
| Height | 1939 mm (76.34 in.) |
| Wheelbase | 3378 mm (132.99 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) | 13.8 m (45.28 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 |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| 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 with the 6.6L Duramax diesel and Allison automatic transmission was a cornerstone of GMC’s heavy-duty truck offerings. Built on the GMT900 platform, this truck was designed to provide substantial improvements in towing capacity, payload, and overall durability compared to its predecessors. The Regular Cab Long Box configuration specifically catered to customers prioritizing functionality and cargo space over passenger comfort. This combination was popular with tradesmen, farmers, and anyone requiring a dependable work truck capable of handling demanding tasks. It represented a significant step forward in diesel truck technology, offering a blend of power and efficiency.
Powertrain & Engine Architecture
At the heart of this Sierra 2500HD lay the Duramax LMM 6.6-liter V8 diesel engine. This engine was a significant refinement of the previous LBZ Duramax, featuring a redesigned combustion chamber and improved fuel injection system. The LMM utilized a common-rail direct injection system, delivering fuel at extremely high pressures for optimized combustion and reduced emissions. The engine produced 365 horsepower at 3200 rpm and a robust 895 lb-ft of torque at 1600 rpm. A variable geometry turbocharger with an intercooler further enhanced performance. The engine’s OHV valvetrain, while traditional, proved to be exceptionally durable. The Allison 1000 six-speed automatic transmission was specifically engineered to handle the immense 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 Allison’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 driving experience markedly different from lighter-duty trucks. Acceleration, while not sporty, was strong and consistent, particularly when leveraging the engine’s substantial torque. The Allison transmission shifted smoothly and decisively, providing ample power for merging onto highways or climbing steep grades, even when heavily loaded. Compared to the gasoline-powered versions of the Sierra 2500HD, the diesel offered significantly more low-end torque, making it ideal for towing. While the manual transmission variants offered a more direct connection to the engine, the Allison automatic provided ease of use and reduced driver fatigue, especially in stop-and-go traffic. The truck’s substantial weight and heavy-duty suspension contributed to a firm ride, but it was well-suited for hauling heavy loads without excessive body roll.
Equipment & Trim Levels
The Sierra 2500HD Regular Cab Long Box with the Duramax/Allison powertrain typically came standard with a relatively utilitarian interior. Standard features included vinyl upholstery, air conditioning, and a basic audio system. However, buyers could opt for a range of upgrades, including cloth or leather upholstery, power windows and locks, a premium audio system, and a navigation system. The work truck (WT) trim was the most basic, while the SLE and SLT trims offered increasing levels of luxury and convenience features. Optional extras included a trailer brake controller, a fifth-wheel hitch preparation package, and various exterior enhancements.
Chassis & Braking
The GMT900 chassis was designed for heavy-duty applications. 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, with ABS as standard equipment. The front discs measured 325x38mm, while the rear discs were 325x30mm. The braking system was adequately sized for the truck’s weight and towing capacity, providing confident stopping power even under heavy loads.
Market Reception & Comparison
The Duramax/Allison combination in the Sierra 2500HD was widely praised by automotive critics and truck enthusiasts alike. It was consistently lauded for its impressive towing capacity, fuel efficiency (for a heavy-duty diesel), and overall reliability. Compared to the gasoline-powered Sierra 2500HD models, the diesel offered significantly better fuel economy and a much higher towing capacity. Compared to competing trucks from Ford and Ram, the GMC Sierra 2500HD with the Duramax engine was often considered to be a top contender, offering a compelling combination of power, refinement, and dependability. Some critics noted the truck’s relatively firm ride, but this was generally accepted as a trade-off for its heavy-duty capabilities.
Legacy
The 2007-2010 GMC Sierra 2500HD with the 6.6L Duramax and Allison automatic transmission has proven to be a remarkably durable and reliable truck. The LMM Duramax engine is generally considered to be one of the most reliable Duramax engines ever produced, with many examples exceeding 200,000 miles with proper maintenance. On the used car market, these trucks continue to command relatively high prices, reflecting their reputation for dependability and their ability to handle demanding tasks. The Allison transmission is also known for its longevity and robustness. Regular maintenance, including oil changes and fuel filter replacements, is crucial for ensuring the long-term health of this powertrain. These trucks remain a popular choice for those seeking a capable and dependable heavy-duty work truck.
