The GMC Sierra 3500HD III, specifically the Crew Cab Long Box configuration powered by the 6.6-liter Duramax TD V8 engine producing 365 horsepower, 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 combined with a degree of passenger comfort. It occupied a premium position within the Sierra 3500HD lineup, offering a powerful diesel option alongside gasoline engines, and catered to customers like contractors, ranchers, and those requiring a robust work truck with family-friendly space.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD III (GMT900) Crew Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (365 Hp) SRW 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, 120.5 Hp/tonne |
| Weight-to-torque ratio | 3.4 kg/Nm, 295.5 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 | 3029 kg (6677.8 lbs.) |
| Max. weight | 4445 kg (9799.55 lbs.) |
| Max load | 1416 kg (3121.75 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%) | 5897 kg (13000.66 lbs.) |
| Length | 6572 mm (258.74 in.) |
| Width including mirrors | 2436 mm (95.91 in.) |
| Height | 1931 mm (76.02 in.) |
| Wheelbase | 4242 mm (167.01 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) | 16.8 m (55.12 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 |
| 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
At the heart of this Sierra 3500HD 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 an improved cooling system. The LMM utilized a common-rail fuel 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. Paired with the engine was the Allison 1000 six-speed automatic transmission, known for its robustness and ability to handle the high torque output of the Duramax. This transmission featured a lock-up torque converter for improved fuel economy at highway speeds.
Driving Characteristics
The 365 horsepower and 895 lb-ft of torque delivered by the LMM Duramax, channeled through the Allison automatic, provided impressive performance for a heavy-duty truck. While not as quick as gasoline-powered counterparts, the Sierra 3500HD offered substantial pulling power and a relaxed driving experience. The Allison transmission’s gear ratios were optimized for towing, providing ample torque in lower gears and comfortable cruising at highway speeds. Compared to the 1.8L gasoline engine options available in the Sierra lineup, the Duramax offered significantly more torque, making it ideal for demanding tasks. However, the diesel’s power delivery was more linear, lacking the immediate responsiveness of the gasoline engines. The automatic transmission, while capable, didn’t offer the driver engagement of a manual transmission.
Equipment & Trim Levels
The Crew Cab Long Box 6.6 Duramax configuration typically came with a well-equipped interior, reflecting its position as a premium trim. Standard features included cloth upholstery, air conditioning, power windows and locks, and a basic audio system. The Crew Cab configuration provided ample space for passengers, making it suitable for families. Optional extras included leather upholstery, a premium Bose audio system, navigation, heated seats, and a sunroof. Exterior features typically included chrome bumpers and grille accents, and alloy wheels were often included or available as an option.
Chassis & Braking
The Sierra 3500HD’s chassis was designed for heavy-duty use. It featured a fully boxed frame for increased rigidity and durability. The front suspension utilized an independent torsion bar setup with double wishbones, providing a comfortable ride while maintaining load-carrying capacity. The rear suspension employed a traditional leaf spring setup, optimized for handling 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. Due to the truck’s weight, rear brakes were slightly smaller than the front brakes.
Market Reception & Comparison
The 6.6 Duramax-equipped Sierra 3500HD received generally positive reviews from critics. The engine was praised for its power, torque, and relatively quiet operation compared to older diesel engines. The Allison transmission was also lauded for its durability and smooth shifting. Fuel economy, while not exceptional, was considered reasonable for a truck of this size and capability. Compared to the gasoline-powered Sierra 3500HD models, the Duramax offered superior towing capacity and fuel efficiency, but came at a higher initial cost. Reliability was generally good, although some owners reported issues with the fuel injection system and turbocharger over the long term.
Legacy
The GMT900-generation Sierra 3500HD, and particularly the 6.6 Duramax-powered variants, have developed a strong following among truck enthusiasts. The LMM Duramax engine is considered a robust and reliable powerplant, and well-maintained examples continue to command respectable prices on the used market. The Allison transmission’s reputation for durability ensures that these trucks remain capable workhorses for years to come. While newer generations of the Sierra 3500HD offer more advanced technology and features, the GMT900 remains a popular choice for those seeking a proven and capable heavy-duty truck.
