The GMC Sierra 2500HD III, specifically the Extended Cab Long Box configuration powered by the 6.0-liter V8 engine producing 360 horsepower, was a prominent model in GMC’s heavy-duty truck lineup from 2007 to 2010. This generation, known as the GMT900, marked a significant advancement in both capability and refinement for GMC, aiming to deliver a robust work truck with a level of comfort and features previously uncommon in the segment. Positioned as a mid-to-upper tier offering within the 2500HD range, it sat above the base work truck models but below the more luxurious Denali trims. This variant was primarily marketed and sold in North America, catering to customers requiring substantial towing and hauling capacity for both professional and recreational needs.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900) Extended Cab Long Box |
| Type (Engine) | 6.0 V8 (360 Hp) 4WD Automatic |
| Start of production | 2007 |
| End of production | 2010 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 2 |
| Fuel Type | Petrol (Gasoline) |
| Weight-to-power ratio | 7.5 kg/Hp, 132.8 Hp/tonne |
| Weight-to-torque ratio | 5.3 kg/Nm, 190 Nm/tonne |
| Power | 360 Hp @ 5400 rpm |
| Power per litre | 60.3 Hp/l |
| Torque | 515 Nm @ 4200 rpm, 379.84 lb.-ft. @ 4200 rpm |
| Maximum engine speed | 6000 rpm |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Vortec LY6 |
| Engine displacement | 5967 cm3, 364.13 cu. in. |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 101.6 mm, 4 in. |
| Piston Stroke | 92 mm, 3.62 in. |
| Compression ratio | 9.6:1 |
| Number of valves per cylinder | 2 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Naturally aspirated engine |
| Valvetrain | OHV |
| Engine oil capacity | 5.7 l, 6.02 US qt | 5.02 UK qt |
| Coolant | 15.5 l, 16.38 US qt | 13.64 UK qt |
| Kerb Weight | 2711 kg, 5976.73 lbs. |
| Max. weight | 4173 kg, 9199.89 lbs. |
| Max load | 1462 kg, 3223.16 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%) | 5579 kg, 12299.59 lbs. |
| Length | 6330 mm, 249.21 in. |
| Width including mirrors | 2436 mm, 95.91 in. |
| Height | 1930 mm, 75.98 in. |
| Wheelbase | 4001 mm, 157.52 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 m, 52.49 ft. |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels permanently, and the front wheels are driven through an electrically or mechanically operated clutch if necessary. |
| Drive wheel | All wheel drive (4×4) |
| Number of gears and type of gearbox | 6 gears, automatic transmission Hydra-Matic |
| 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 core of this Sierra 2500HD variant is the Vortec LY6 6.0-liter V8 engine. This engine belongs to the Vortec family, renowned for its robust construction and relatively straightforward design. The LY6 features a cast iron block and aluminum cylinder heads, contributing to its long-term durability. It boasts a 9.6:1 compression ratio and utilizes a multi-port fuel injection system. The overhead valve (OHV) valvetrain, while not as sophisticated as overhead cam designs, proved to be reliable and delivered ample low-end torque. The engine’s 360 horsepower and 515 lb-ft of torque are channeled to the wheels through a six-speed Hydra-Matic automatic transmission. This transmission was selected for its ability to manage the substantial torque output of the V8 and provide smooth, predictable gear changes. The 4WD system incorporated a shift-on-the-fly mechanism, enabling drivers to easily switch between two-wheel drive and four-wheel drive based on prevailing road conditions.
Driving Characteristics
The combination of the 6.0L V8 and six-speed automatic in the Sierra 2500HD offered a balance between power and usability. While not as quick as some of the lighter-duty trucks or those equipped with the optional Duramax diesel engine, the 360 hp variant provided sufficient power for towing and hauling substantial loads. The automatic transmission’s gear ratios were optimized for towing, providing strong acceleration from a standstill and maintaining comfortable cruising speeds on the highway. Compared to the manual transmission options, the automatic offered greater convenience, especially in congested traffic. However, it did result in a slight decrease in fuel economy and a less direct connection to the engine. The truck’s considerable weight (approximately 6,000 lbs) was noticeable, but the robust suspension and powerful engine helped to mitigate this.
Equipment & Trim Levels
The Extended Cab Long Box 6.0L 4WD Sierra 2500HD typically came standard with features such as air conditioning, power windows and locks, a basic audio system, and vinyl upholstery. The extended cab offered additional rear seating, although legroom was somewhat limited. Optional extras included upgraded audio systems, leather upholstery, power-adjustable seats, a navigation system, and various towing packages. The exterior generally featured chrome bumpers and grille accents, and buyers could choose features like running boards and a spray-in bedliner. This trim level occupied a comfortable position in the middle of the Sierra 2500HD lineup, providing a good balance of features and affordability.
Chassis & Braking
The GMT900 chassis featured a fully boxed frame engineered for strength and rigidity. The front suspension utilized an independent torsion bar setup with double wishbone control arms, delivering a comfortable ride and good handling. The rear suspension employed a traditional leaf spring setup, optimized for load-carrying capacity. Braking was provided by ventilated disc brakes on all four wheels, with ABS (Anti-lock Braking System) standard. The front discs measured 325x38mm, while the rear discs were 325x30mm. The steering system was a cone worm with recirculation balls, providing a solid and predictable feel.
Market Reception & Comparison
The GMC Sierra 2500HD with the 6.0L V8 and automatic transmission was generally well-received by both automotive critics and consumers. It was praised for its strong towing capacity, comfortable ride, and relatively affordable price point. Compared to the diesel-powered Duramax models, the 6.0L V8 offered a lower initial cost but sacrificed fuel economy and ultimate towing power. Against competitors like the Ford Super Duty and Ram 2500, the Sierra 2500HD held its own, offering a compelling combination of features and performance. Fuel economy was typical for a heavy-duty truck of this era, averaging around 12-15 mpg in mixed driving conditions.
Legacy
The Vortec LY6 6.0L V8 proved to be a durable and reliable engine, and numerous examples are still in operation today. While not entirely without potential issues (such as Active Fuel Management system problems in some cases), the engine is generally considered relatively easy to maintain and repair. The GMT900 Sierra 2500HD remains a popular choice for those seeking a capable and affordable heavy-duty truck. In the used car market, these trucks typically command reasonable prices, making them an attractive option for buyers who need a workhorse without a significant financial investment. The combination of a robust powertrain, a comfortable interior, and a strong chassis has ensured that the Sierra 2500HD III continues to be a respected and valued truck among owners and enthusiasts.
