The GMC Sierra 2500HD III, specifically the Regular Cab Long Box configuration powered by the 6.6-liter Duramax turbodiesel V8 engine producing 365 horsepower and paired with a four-wheel-drive system and automatic transmission, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2007 to 2010 as part of the GMT900 platform generation, this variant was aimed at buyers needing substantial towing and hauling capacity, blending robust diesel power with the convenience of an automatic transmission and the versatility of a four-wheel-drive system. It occupied a strong position within the 2500HD lineup, offering a step up in capability from the gasoline-powered engines while remaining a more accessible option than the fully-equipped 3500HD models.
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) 4WD 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 | 7.8 kg/Hp, 127.9 Hp/tonne |
| Weight-to-torque ratio | 3.2 kg/Nm, 313.7 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 | 2853 kg (6289.79 lbs.) |
| Max. weight | 4173 kg (9199.89 lbs.) |
| Max load | 1320 kg (2910.1 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 | 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 |
INTRODUCTION
The 2007-2010 GMC Sierra 2500HD with the 6.6L Duramax diesel and automatic transmission was a workhorse designed for demanding tasks. Built on the GMT900 platform, this generation represented a significant upgrade in terms of capability and refinement compared to its predecessors. The Regular Cab Long Box configuration prioritized cargo space and towing capacity, making it a popular choice for commercial users, farmers, and those requiring a heavy-duty truck for frequent hauling. This specific combination of engine, transmission, and drivetrain aimed to deliver a balance of power, usability, and dependability.
Powertrain & Engine Architecture
At the heart of this Sierra 2500HD lies the Duramax LMM 6.6-liter V8 diesel engine. This engine is a turbocharged and intercooled design, utilizing a common-rail direct fuel injection system to optimize combustion efficiency and power delivery. The LMM engine produced 365 horsepower at 3200 rpm and a substantial 895 lb-ft of torque at 1600 rpm. The engine features an overhead valve (OHV) valvetrain and a robust cast iron block. The Allison 1000 six-speed automatic transmission was specifically designed to handle the high torque output of the Duramax engine. This transmission featured electronically controlled shifting and a heavy-duty torque converter, ensuring smooth and reliable operation even under heavy loads. The 4WD system employed an electronically controlled transfer case, allowing the driver to switch between two-wheel drive and four-wheel drive modes as needed.
Driving Characteristics
The 6.6L Duramax with the Allison automatic provided a surprisingly refined driving experience for a heavy-duty truck. While not as quick as gasoline-powered counterparts, the immense torque available from low engine speeds allowed for effortless towing and hauling. The Allison transmission shifted smoothly and intelligently, minimizing gear hunting and maximizing fuel efficiency. Compared to the manual transmission options, the automatic offered greater convenience, particularly in stop-and-go traffic. However, some drivers preferred the more direct control offered by a manual gearbox. The long box configuration provided ample cargo space, but it also resulted in a longer wheelbase, which could make maneuvering in tight spaces more challenging. The ride quality, while improved over previous generations, remained firm due to the heavy-duty suspension.
Equipment & Trim Levels
The Sierra 2500HD Regular Cab Long Box with the Duramax engine typically came with a fairly comprehensive list of standard features. These included air conditioning, power windows and locks, and a basic audio system. Higher trim levels, such as the SLT, added features like leather upholstery, heated seats, a premium audio system, and chrome exterior trim. Optional extras included a navigation system, a sunroof, and various towing packages. The interior was functional and durable, designed to withstand the rigors of heavy-duty use. The dashboard layout was straightforward and easy to use, with large, clearly marked controls.
Chassis & Braking
The GMT900 chassis featured a fully boxed frame for increased rigidity and strength. The front suspension utilized an independent torsion bar setup with double wishbone control arms, while the rear suspension employed a traditional leaf spring design. This combination provided a good balance of ride comfort and load-carrying capacity. The braking system consisted of ventilated disc brakes on all four wheels, with ABS (Anti-lock Braking System) as standard equipment. The front brakes measured 325x38mm, while the rear brakes were slightly smaller at 325x30mm. The steering system was a cone worm type with recirculation balls, providing precise and responsive steering feel.
Market Reception & Comparison
The 2007-2010 GMC Sierra 2500HD with the Duramax diesel engine was generally well-received by critics and consumers alike. It was praised for its powerful engine, smooth transmission, and robust construction. Compared to the gasoline-powered versions of the Sierra 2500HD, the Duramax offered significantly more torque and better fuel economy when towing heavy loads. However, the diesel engine also came with a higher price tag and potentially higher maintenance costs. Compared to the Ford Super Duty and Ram 2500/3500, the Sierra 2500HD was often seen as a more refined and comfortable option, although some competitors offered slightly higher towing capacities.
Legacy
The Duramax LMM engine and Allison transmission combination proved to be exceptionally durable and reliable. Many of these trucks are still on the road today, logging hundreds of thousands of miles. While some maintenance issues, such as injector failures and turbocharger problems, are common with high-mileage Duramax engines, these are generally manageable with proper maintenance. The 2007-2010 Sierra 2500HD remains a popular choice in the used truck market, particularly among those seeking a capable and dependable work truck. Its strong resale value is a testament to its enduring quality and reputation.
