GMC's modern full-size pickup has been around in one form or another since the early '60s. Now into its sixth generation, the Sierra, as it's now called, boasts classic styling and some of the most powerful drivetrains available anywhere. A perennial competitor to the full-size offerings from Ford and Dodge, GMC positions itself as the "professional grade" truck in GM's lineup. Although its sales numbers are far below those of its competitors, when combined with its sister vehicle, the Chevrolet Silverado, the GM trucks sell in competitive numbers to Ford's F-Series.

Often first to market with exclusive features, the Sierra continues that tradition with options like XM Satellite Radio and Bose audio systems. GMC trucks also offer the OnStar communications system that provides the convenience of 24-hour on-call assistance for everything from tow truck requests to dinner reservations. Between its potent Duramax diesel and strong gas V8s, the Sierra one-ton can tackle just about any hard-core towing and hauling duties you could throw at it. Combine this with sharp styling on the outside and plenty of available features on the inside, and the Sierra 3500 presents a compelling package for anyone in the market for a no-holds-barred work truck.

As capable as it is, the Sierra is starting to show its age while its competition has been slowly upgrading its offerings. Both Dodge and Ford offer more powerful engine options as well as more refined interiors. Needless to say, it's worth shopping around before settling on the Sierra.

The 3500 is only available as a long box, but buyers can still choose between regular, extended- and crew-cab body styles and either two- or four-wheel drive (regular cabs are 4WD only). There are several trim levels: Work Truck, SL1, SLE1, SLE2 and SLT. Work Trucks are intended for jobsite use and offer basics like 16-inch steel wheels, a vinyl 40/20/40-split bench seat, dual-zone manual air conditioning and an AM/FM radio. SL1 models add chrome-finish wheels, grille and bumpers, cloth upholstery, cruise control and a CD player. SLE1 models add foglights, privacy glass, power windows and door locks, keyless entry, power-heated exterior mirrors and a leather-wrapped steering wheel. SLE2 models provide a six-way power driver seat and an upgraded Bose stereo. Top-of-the-line SLTs add leather bucket seats with heaters and dual 10-way power adjustments, driver-seat memory, automatic climate control, power-retractable mirrors, an in-dash CD changer, steering wheel audio controls and a trip computer.

The 3500's base engine is a 6.0-liter V8 rated at 300 horsepower and 360 pound-feet of torque. If that's not enough grunt under the hood for you, GMC offers two more powerful options: an 8.1-liter V8 and a 6.6-liter "Duramax" turbodiesel V8. The 8.l-liter engine boasts an impressive 330 hp and 450 lb-ft of torque, while the diesel makes 360 hp and 650 lb-ft of torque. The standard transmission for the 6.0-liter V8 is a five-speed manual with a four-speed automatic optional. The 8.1-liter V8 and 6.6-liter diesel can be hooked up to either a six-speed manual or a heavy-duty Allison six-speed automatic. Properly equipped, the Sierra 3500 can tow 12,000 pounds.

Four-wheel antilock disc brakes are standard. In government crash tests, the Sierra earned a four-star rating (out of five) for driver protection in frontal impacts and three stars for the front passenger. In frontal offset crash testing, the Sierra was given an overall rating of "Marginal," the second lowest on a scale of four.

The 3500 is a dedicated work truck, so don't expect the plush ride of its light-duty siblings. Any of the three available engines provide swift acceleration and ample towing power, but the 6.6-liter turbodiesel is the best choice for those who tow heavy loads. The manual transmissions are about what you would expect in a big truck, but the automatics shift smoothly and crisply no matter how heavy the load.

Inside, Sierra buyers will find a logically laid-out interior with an easy-to-use dual-zone climate control system and clear, uncluttered gauges. Materials quality is unimpressive, and build quality, though improved over the last few years, is still below the competition. Extended cabs and crew cabs offer large cabins with plenty of room and, on higher trims, comfortable bucket seats.