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 blend of increased capability, refined comfort, and updated technology. Within the 2500HD range, the Crew Cab Standard Box configuration with the 6.6-liter Duramax turbodiesel V8 engine producing 365 horsepower and paired with a 6-speed Allison automatic transmission, occupied a sweet spot for buyers needing substantial towing and hauling capacity without sacrificing everyday usability. This variant was positioned as a premium offering, appealing to those who required a robust work truck but also desired a comfortable and well-equipped cabin for both work and family use.
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) 4WD 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 | 8.3 kg/Hp, 120.7 Hp/tonne |
| Weight-to-torque ratio | 3.4 kg/Nm, 295.9 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 | 3025 kg (6668.98 lbs.) |
| Max. weight | 4173 kg (9199.89 lbs.) |
| Max load | 1148 kg (2530.91 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 | All wheel drive (4×4). ICE drives rear wheels, front wheels engaged via clutch. |
| 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 |
Powertrain & Engine Architecture
The heart of this Sierra 2500HD variant is the Duramax LMM 6.6-liter V8 diesel engine. This engine represented a significant refinement of the previous LBZ Duramax, incorporating a more robust block, improved cylinder heads, and a revised 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 featured an electronically controlled variable geometry turbocharger (VGT) and an intercooler to maximize power and efficiency. The overhead valve (OHV) valvetrain, while traditional, proved durable and reliable. The Allison 1000 6-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 economy at highway speeds and provided smooth, responsive shifting.
Driving Characteristics
The combination of the 365-horsepower Duramax engine and the Allison automatic transmission delivered a compelling driving experience. While not as overtly quick as gasoline-powered trucks, the Sierra 2500HD offered prodigious low-end torque – 895 lb-ft – making it exceptionally capable for towing and hauling heavy loads. The Allison transmission’s gear ratios were well-matched to the engine’s powerband, providing ample power for both city driving and highway cruising. Compared to the 1.8L gasoline engine options available in the Sierra 1500, this diesel offered a vastly different character, prioritizing torque over outright acceleration. The automatic transmission, while convenient, did result in a slight reduction in fuel economy compared to the available manual transmission, but the trade-off in ease of use was often considered worthwhile by many buyers.
Equipment & Trim Levels
The Crew Cab Standard Box 2500HD with the Duramax engine typically came well-equipped, even in its base trim. Standard features included air conditioning, power windows and locks, a CD player, and cloth upholstery. Higher trim levels, such as the LT and LTZ, 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 provided ample space for passengers, making it a comfortable choice for families or crews.
Chassis & Braking
The GMT900 chassis was designed for heavy-duty use. The front suspension utilized an independent torsion bar setup with double wishbones, providing a comfortable ride while maintaining robust load-carrying capacity. The rear suspension employed a traditional leaf spring setup, optimized for durability and stability under heavy loads. Braking duties were handled by ventilated disc brakes on all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) was standard. The robust frame and suspension components allowed for a substantial payload capacity and impressive towing capabilities.
Market Reception & Comparison
The Duramax-equipped Sierra 2500HD was generally well-received by critics and consumers alike. It was praised for its powerful engine, smooth-shifting transmission, and comfortable ride. Compared to the gasoline-powered Sierra 2500HD models, the Duramax offered significantly better fuel economy when towing and hauling, as well as superior torque. While the initial cost of the Duramax engine was higher, the long-term benefits in terms of fuel savings and resale value often outweighed the upfront expense. Compared to competing heavy-duty trucks from Ford and Ram, the Sierra 2500HD was often seen as a strong contender, offering a compelling combination of capability, comfort, and reliability.
Legacy
The Duramax LMM engine, paired with the Allison transmission, has proven to be a remarkably durable and reliable powertrain. Well-maintained examples of the 2007-2010 Sierra 2500HD continue to command strong prices in the used car market. The engine is known for its longevity, with many examples exceeding 200,000 miles with proper maintenance. Common maintenance items include regular oil changes, fuel filter replacements, and occasional injector cleaning. The GMT900 platform, and specifically this Duramax/Allison combination, remains a popular choice for those seeking a capable and dependable heavy-duty truck.
