The GMC Sierra 3500HD, specifically the V (GMTT1XX) Double Cab Long Bed configuration powered by the 6.6-liter Duramax TD V8 producing 445 horsepower, represents a significant offering in the heavy-duty pickup truck segment. Produced from 2020 through 2023, this variant aimed to provide a balance of robust towing capability, diesel efficiency, and passenger comfort within the Sierra 3500HD lineup. It occupied a position as a workhorse trim, appealing to buyers needing substantial payload and towing capacity without necessarily opting for the highest luxury appointments found in Denali trims.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD V (GMTT1XX) Double Cab Long Bed |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) SRW Automatic |
| Start of production | 2020 |
| End of production | 2023 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 7.8 kg/Hp, 127.7 Hp/tonne |
| Weight-to-torque ratio | 2.8 kg/Nm, 354.1 Nm/tonne |
| Power | 445 Hp @ 2800 rpm |
| Power per litre | 67.4 Hp/l |
| Torque | 1234 Nm @ 1600 rpm (910.15 lb.-ft. @ 1600 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Duramax L5P |
| Engine displacement | 6604 cm3 (403 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 | 16:1 |
| 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 | 29.1 l (30.75 US qt | 25.6 UK qt) |
| Kerb Weight | 3485 kg (7683.11 lbs.) |
| Max. weight | 5375 kg (11849.85 lbs.) |
| Max load | 1890 kg (4166.74 lbs.) |
| Fuel tank capacity | 136 l (35.93 US gal | 29.92 UK gal) |
| Permitted trailer load with brakes (12%) | 6577 kg (14499.8 lbs.) |
| Length | 6514 mm (256.46 in.) |
| Width including mirrors | 2079 mm (81.85 in.) |
| Height | 2054 mm (80.87 in.) |
| Wheelbase | 4127 mm (162.48 in.) |
| Front track | 1731 mm (68.15 in.) |
| Rear (Back) track | 1736 mm (68.35 in.) |
| Ride height (ground clearance) | 284 mm (11.18 in.) |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels of the vehicle. |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 10 gears, automatic transmission Allison |
| Front suspension | Coil spring, Double wishbone, Transverse stabilizer |
| Rear suspension | Rigid axle suspension, Leaf spring |
| Front brakes | Ventilated discs, 350×40 mm |
| Rear brakes | Ventilated discs, 355×40 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Electric Steering |
| Tires size | 265/70 R17; 245/75 R17; 265/70 R18; 265/60 R20 |
| Wheel rims size | 7.5J x 17; 8J x 18; 8.5J x 20 |
Introduction
The 2020-2023 GMC Sierra 3500HD Double Cab Long Bed with the 6.6L Duramax diesel and 10-speed Allison automatic transmission is a heavy-duty pickup truck designed for demanding tasks. Built on the GMTT1XX platform, this generation Sierra 3500HD represented a significant overhaul of GMC’s heavy-duty lineup, focusing on increased capability, improved technology, and enhanced interior refinement. The Double Cab configuration offered a balance between passenger space and bed length, making it suitable for both work and family use. This particular variant, with its potent diesel engine and automatic transmission, was positioned as a strong contender for buyers who frequently tow large trailers or haul heavy loads.
Powertrain & Engine Architecture
At the heart of this Sierra 3500HD lies the Duramax L5P 6.6-liter turbocharged diesel V8 engine. This engine is a cornerstone of GMC’s heavy-duty offerings, known for its durability and impressive torque output. The L5P utilizes a cast iron block, aluminum cylinder heads, and a robust crankshaft designed to withstand the stresses of heavy-duty operation. The engine employs a high-pressure common rail direct fuel injection system, delivering fuel directly into the cylinders for optimized combustion. The turbocharger, coupled with an intercooler, provides increased air intake, boosting power and efficiency. The valvetrain utilizes a pushrod (OHV) design, a traditional choice for diesel engines prioritizing low-end torque. The 10-speed Allison automatic transmission is a key component, providing smooth and efficient power delivery. This transmission features electronically controlled shifts and a wide gear ratio spread, optimizing performance for both towing and everyday driving.
Driving Characteristics
The combination of the 445 horsepower and 910 lb-ft of torque from the Duramax engine, paired with the 10-speed Allison transmission, delivers a commanding driving experience. While not as quick off the line as gasoline-powered trucks, the Sierra 3500HD excels in situations requiring substantial pulling power. The 10-speed transmission allows the engine to stay within its optimal power band, even when towing heavy loads. Compared to the 6.6L gasoline engine option, the Duramax provides significantly more torque at lower RPMs, making it ideal for towing. Compared to higher-output Duramax variants (available in some trims), this 445 hp version offers a slightly more relaxed driving experience, prioritizing fuel economy and longevity over outright acceleration. The gear ratios are tuned for maximizing towing capacity and minimizing strain on the powertrain.
Equipment & Trim Levels
The Sierra 3500HD Double Cab Long Bed with the Duramax engine typically came standard with a respectable array of features. These included air conditioning, power windows and locks, a basic infotainment system with a touchscreen display, and a rearview camera. Interior upholstery was typically cloth or vinyl, with options for leather upgrades available. The dashboard layout was functional and straightforward, prioritizing ease of use. Optional extras included a premium audio system, navigation, heated and ventilated front seats, a power-adjustable steering column, and advanced safety features like lane departure warning and automatic emergency braking. The Double Cab configuration offered comfortable seating for five passengers, with ample legroom in both rows.
Chassis & Braking
The Sierra 3500HD’s chassis is built for durability and heavy-duty use. It features a fully boxed frame constructed from high-strength steel. The front suspension utilizes a coil spring, double wishbone design with a transverse stabilizer bar, providing a comfortable ride and stable handling. The rear suspension employs a traditional leaf spring setup, optimized for carrying heavy loads. Braking duties are handled by ventilated disc brakes on all four wheels, providing ample stopping power even when towing. The rear brakes are slightly larger in diameter than the front. An Anti-lock Braking System (ABS) is standard, enhancing safety and control during emergency braking situations.
Market Reception & Comparison
The GMC Sierra 3500HD with the Duramax diesel engine consistently received positive reviews from automotive critics. It was praised for its powerful engine, smooth transmission, and impressive towing capacity. Fuel economy, while not exceptional, was considered competitive for a heavy-duty pickup truck. Compared to the gasoline-powered Sierra 3500HD, the Duramax diesel offered significantly better fuel economy when towing. Compared to other heavy-duty trucks like the Ford Super Duty and Ram 3500, the Sierra 3500HD was often seen as a well-rounded option, offering a good balance of capability, comfort, and refinement. Some critics noted that the interior, while improved, wasn’t quite as luxurious as some of its competitors.
Legacy
The Duramax L5P engine and Allison 10-speed transmission have proven to be a reliable and durable powertrain combination. These trucks have maintained strong resale values in the used car market, reflecting their reputation for dependability and capability. Properly maintained, these engines can easily exceed 200,000 miles. Common maintenance items include regular oil changes, fuel filter replacements, and coolant flushes. The GMTT1XX generation Sierra 3500HD represents a significant step forward in heavy-duty truck technology, offering a compelling combination of power, efficiency, and refinement that continues to appeal to buyers today.
