It may look like last year’s model, but the 2011 GMC Sierra 2500HD pickup is stuffed with improvements beneath the surface. A strengthened frame, a more powerful engine, upgraded suspension, increased capabilities – these are just some of the changes that will keep the Sierra 2500HD in the upper echelon of heavy-duty trucks for 2011.

The Sierra 2500HD is offered with a Regular cab (available only with an 8-foot long bed) or an Extended or Crew cab (with a 6.5-foot standard bed also available). The trim levels are now topped by a fashionable Denali option – a first for the Sierra line – that is easily recognized by the chrome dripping from its exterior. If you want to go in the other direction, there’s the utilitarian Work Truck trim. The SLE and SLT trims offer a middle ground. Rear-wheel drive is standard, and four-wheel drive is optional for all versions of the truck.

The standard powertrain for the Sierra 2500HD is a 6.0-liter V8 (360 hp, 380 lb-ft of torque) with a six-speed automatic transmission. However, the optional 6.6-liter Duramax turbodiesel V8 and its sturdier six-speed automatic transmission with manual mode is the choice attracting attention. This clean diesel combination produces 397 horsepower and 765 lb-ft of torque - 105 lb-ft more than last year’s diesel.

Sixty percent of the parts in the diesel engine are new, which helps make it 11 percent more fuel efficient than the previous version, according to its manufacturers. It also runs cleaner, thanks to a new two-stage exhaust gas recirculation system and the use of selective catalytic reduction (SCR). The SCR system uses diesel exhaust fluid (DEF) that must be monitored by the owner. There are plenty of automatic warnings and messages, but if the DEF runs down to a 100-mile range or below, the truck’s speed will become limited, first to 55 mph and then decelerating all the way to just 5 mph.

The Sierra 2500HD powertrains also get new glow plugs (said to start cold in seconds, even in temperatures of 20 below), a revised engine block (to reduce vibration and handle increased torque levels), a larger fuel tank (36 gallons now to extend driving range) and a new flat-panel air filter (to improve cold-weather air intake).

And that’s not the end of the new mechanical features. There’s also a brand new fully boxed frame that is stronger and stiffer to handle the increased pay- and tow loads offered by the new engine and to help reduce vibration and driving harshness. The suspension is loaded with upgraded components (forged steel front upper control arm, bolstered cast-iron front lower bar, new shocks and shock attachments) for a smoother ride on the highway or on the farm with a full load in the back.

Maximum payloads and towing capacities vary by configuration, and the top end for the Sierra 2500HD is a 3,704-maximum payload and a 13,000-pound towing capacity with a standard ball hitch. That towing number jumps to 16,500 pounds with a fifth-wheel connection. Handling large loads with the Sierra 2500HD is easier with the addition of GM’s trailer sway control, which uses the truck’s antilock braking system (complete with larger brakes to also help handle the larger loads) and the integrated trailer brake controller to brake individual wheels on the truck as necessary.

The new Sierra 2500HD’s interior, unlike its underpinnings, is almost the same as it was last year. The controls are straightforward and well placed, the front seats are very comfortable, and the Extended cab seating is fine for adults, but the Crew cab is really the choice if you’re going to have passengers in the rear on a regular basis.

The Work Truck trim is pretty basic and has vinyl upholstery and steel wheels, but it does come with air conditioning, a trip computer, tilt steering wheel and a four-speaker radio (no CD). The SLE trim adds alloy wheels, cloth upholstery, cruise control and a CD player. The SLT is available only with an Extended or Crew cab and adds an automatic locking rear differential, heavy-duty trailering package, a Bose stereo system, heated leather seats, remote start, heated mirrors and foglights.

The Denali trim comes only as a four-wheel-drive Crew cab. It’s exterior is marked with a unique four-bar chrome grille, chrome door handles, chrome accents, body-color bumpers and 20-inch polished forged aluminum wheels. Other upgrades include skid plates, rear parking sensors, EZ-lift tailgate, power-adjustable pedals, 12-way power front seats, a premium Bose sound system and brushed aluminum trim.