The GMC Sierra 3500HD III, produced between 2007 and 2010, marked a significant advancement in GMC’s heavy-duty truck offerings. As part of the GMT900 generation, this Sierra 3500HD was available in various configurations, notably the Extended Cab with a Long Box, catering to customers requiring substantial towing and hauling capacity. The variant featuring the 6.6-liter Duramax turbodiesel V8 engine, producing 365 horsepower, coupled with a six-speed Allison automatic transmission and a four-wheel-drive system, proved particularly popular among those prioritizing serious performance. This configuration represented the top tier of the Sierra 3500HD lineup, balancing power, refinement, and capability.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD III (GMT900) Extended Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (365 Hp) 4WD SRW Automatic |
| Start of production | 2007 |
| End of production | 2010 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.5 kg/Hp, 118.1 Hp/tonne |
| Weight-to-torque ratio | 3.5 kg/Nm, 289.6 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 | 3091 kg (6814.49 lbs.) |
| Max. weight | 4490 kg (9898.76 lbs.) |
| Max load | 1399 kg (3084.27 lbs.) |
| Trunk (boot) space – maximum | 2170 l (76.63 cu. ft.) |
| Fuel tank capacity | 129 l (34.08 US gal | 28.38 UK gal) |
| Permitted trailer load with brakes (12%) | 5488 kg (12098.97 lbs.) |
| Length | 6330 mm (249.21 in.) |
| Width including mirrors | 2436 mm (95.91 in.) |
| Height | 1927 mm (75.87 in.) |
| Wheelbase | 4001 mm (157.52 in.) |
| Front track | 1742 mm (68.58 in.) |
| Rear (Back) track | 1676 mm (65.98 in.) |
| Ride height (ground clearance) | 233 mm (9.17 in.) |
| Minimum turning circle (turning diameter) | 16 m (52.49 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 | 265/75 R16; 265/70 R17; 225/75 R17 |
| Wheel rims size | 6.5J x 17; 7J x 16; 7.5J x 17 |
Powertrain & Engine Architecture
The core of this Sierra 3500HD variant is the Duramax LMM 6.6-liter V8 turbodiesel engine. This engine represented an evolution of the preceding LBZ Duramax, incorporating a strengthened crankshaft, redesigned pistons, and an enhanced cooling system. The LMM utilized a common-rail direct fuel injection system, delivering fuel at exceptionally high pressures for optimized combustion efficiency. The engine’s valvetrain employed an overhead valve (OHV) configuration, favored for its inherent simplicity and durability. A variable geometry turbocharger and intercooler further boosted performance and efficiency. The Allison 1000 six-speed automatic transmission was specifically engineered to manage the substantial torque output of the Duramax engine. This transmission featured a lock-up torque converter for improved fuel economy and a robust cooling system to prevent overheating during demanding operations.
Driving Characteristics
The 365 horsepower and 895 lb-ft of torque generated by the Duramax/Allison pairing equipped the Sierra 3500HD with remarkable towing and hauling capabilities. While not offering the same acceleration as gasoline-powered counterparts, the diesel engine’s abundant low-end torque made it exceptionally well-suited for moving substantial loads. The Allison transmission’s six forward gears allowed for a relatively relaxed cruising speed, even while towing. Compared to the 1.8L gasoline engine options found in lighter-duty Sierra models, this diesel variant delivered a markedly different driving experience, prioritizing power and capability over outright speed. The automatic transmission, while smooth, didn’t provide the same level of driver engagement as a manual transmission, but it simplified operation, particularly in congested traffic or during towing maneuvers.
Equipment & Trim Levels
The Sierra 3500HD offered a spectrum of trim levels, with the Duramax/Allison combination typically found in the higher trims such as LT and SLT. Standard features included air conditioning, power windows and locks, and a basic audio system. Higher trims added amenities like leather upholstery, heated seats, a premium audio system, and navigation. Optional extras encompassed a sunroof, upgraded wheels, and various towing packages. The Extended Cab configuration provided increased passenger space compared to the standard cab, making it a more comfortable choice for families or work crews.
Chassis & Braking
The Sierra 3500HD’s chassis was engineered to withstand the rigors of heavy-duty applications. It featured a fully boxed frame and a robust suspension system. The front suspension utilized an independent torsion bar setup with double wishbones, while the rear suspension employed a conventional leaf spring design. Brakes consisted of ventilated discs at all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) was standard equipment. Due to the increased weight of the Duramax-equipped models, they often incorporated heavier-duty suspension components and larger brakes compared to lighter-duty trims.
Market Reception & Comparison
The Duramax/Allison combination garnered widespread acclaim from automotive reviewers for its performance, dependability, and towing prowess. It quickly became a favored choice among truck enthusiasts and commercial users. In comparison to other heavy-duty trucks of the era, the Sierra 3500HD offered a competitive blend of power, refinement, and value. While the Ford Super Duty and Ram trucks also offered potent diesel engines, the GMC Sierra 3500HD distinguished itself with its smooth ride quality and well-appointed interior. Fuel economy, while not a primary consideration for heavy-duty truck buyers, was respectable for a vehicle of this size and capability.
Legacy
The GMT900-generation Sierra 3500HD, particularly the Duramax/Allison variant, has proven to be a durable and reliable truck. These trucks remain commonly found in the used vehicle market today, often with substantial mileage but still capable of handling demanding tasks. The Duramax LMM engine is renowned for its longevity, and with diligent maintenance, can readily surpass 200,000 miles. The Allison transmission is also highly regarded for its robustness. However, prospective buyers should be mindful of potential issues such as injector failure and turbocharger wear. Overall, the 2007-2010 GMC Sierra 3500HD equipped with the 6.6-liter Duramax engine continues to be a popular and capable heavy-duty truck, representing a compelling combination of reliability, performance, and value.
