The GMC Sierra 2500HD III, specifically the Crew Cab Long Box configuration powered by the 6.6-liter Duramax turbodiesel V8 producing 365 horsepower and paired with a 4WD automatic transmission, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2007 to 2010 (GMT900 platform), this variant aimed to deliver a balance of robust towing capability, comfortable interior space, and refined diesel performance for the North American market. It occupied a sweet spot in the Sierra 2500HD lineup, offering a step up in power and capacity from the gasoline engine options while remaining more accessible than the higher-output Duramax variants.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900) Crew Cab Long 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 | 8.5 kg/Hp, 117.2 Hp/tonne |
| Weight-to-torque ratio | 3.5 kg/Nm, 287.3 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 | 3115 kg (6867.4 lbs.) |
| Max. weight | 4173 kg (9199.89 lbs.) |
| Max load | 1058 kg (2332.49 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 | 6572 mm (258.74 in.) |
| Width including mirrors | 2436 mm (95.91 in.) |
| Height | 1930 mm (75.98 in.) |
| Wheelbase | 4242 mm (167.01 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) | 16.8 m (55.12 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
At the heart of this Sierra 2500HD variant lies the Duramax LMM 6.6-liter V8 diesel engine. This engine represented a refinement of the previous LBZ Duramax, incorporating a more robust crankshaft, redesigned pistons, and improved cooling systems. The LMM utilized a common-rail fuel injection system, delivering fuel at extremely high pressures for optimized combustion and reduced emissions. The turbocharger, coupled with an intercooler, provided increased air intake, boosting power and torque. The engine’s overhead valve (OHV) configuration, while traditional, proved durable and reliable. The Allison 1000 six-speed automatic transmission was specifically designed to handle the substantial torque output of the Duramax engine. This transmission featured a lock-up torque converter for improved fuel efficiency at highway speeds and provided smooth, responsive shifting.
Driving Characteristics
The 365 horsepower and 895 lb-ft of torque delivered by the LMM Duramax, when channeled through the Allison automatic, provided impressive towing and hauling capabilities. While not as overtly powerful as some of the higher-output Duramax configurations, this setup offered a more relaxed and manageable driving experience. The automatic transmission’s gear ratios were optimized for both low-end grunt and comfortable cruising. Acceleration was brisk, but the focus was clearly on providing ample torque for demanding tasks. Compared to the gasoline-powered Sierra 2500HD models, the diesel offered significantly more low-end power and superior fuel economy, especially when towing. Manual transmission equipped Duramax models offered slightly more direct control, but the Allison automatic provided convenience and ease of use, particularly in stop-and-go traffic.
Equipment & Trim Levels
The Crew Cab Long Box configuration, combined with the Duramax engine, typically fell into the mid-to-upper trim levels of the Sierra 2500HD lineup. Standard features included air conditioning, power windows and locks, a CD player, and cloth upholstery. Higher trim levels added features such as leather seats, a Bose sound system, navigation, and heated seats. The spacious Crew Cab provided ample room for passengers, making it a popular choice for families and work crews. Optional extras included a sunroof, upgraded wheels, and various towing packages.
Chassis & Braking
The Sierra 2500HD III featured a robust chassis designed to withstand the stresses of heavy-duty use. 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. An Anti-lock Braking System (ABS) was standard equipment. The heavy-duty suspension and braking system were crucial for managing the truck’s substantial weight and providing safe and controlled operation, even when fully loaded or towing.
Market Reception & Comparison
The 2007-2010 GMC Sierra 2500HD with the 6.6L Duramax and Allison automatic received generally positive reviews. Critics praised its powerful engine, smooth transmission, and comfortable ride. Fuel economy was considered good for a heavy-duty truck, especially when compared to gasoline alternatives. Compared to the Ford Super Duty and Ram 2500, the Sierra 2500HD was often lauded for its refined interior and quiet cabin. However, some reviewers noted that the Duramax engine could be expensive to maintain, particularly the emissions control systems. Reliability was generally good, but issues with the fuel injectors and turbocharger were occasionally reported.
Legacy
The Duramax LMM engine, paired with the Allison automatic transmission, has proven to be a durable and reliable powertrain. These trucks remain popular in the used market, particularly among those seeking a capable and dependable work truck. While older models may require some maintenance, the Duramax engine is known for its longevity and ability to withstand high mileage. The 2007-2010 Sierra 2500HD represents a well-rounded and capable heavy-duty truck that continues to provide value to owners today. The combination of power, comfort, and towing capacity has cemented its place as a respected performer in the heavy-duty truck segment.
