The most striking feature of the 2008 Sierra 1500, which GMC completely redesigned a year ago, is the interior. The new cabin offered on the top SLT trim is similar to that currently offered on GM's full-size sport-utility vehicles such as the GMC Yukon and offers standard luxury features like power heated front leather seats, six-disc CD/MP3-capable audio system, satellite radio, and heated windshield washers, while top crew cab SLT models add rain-sensing wipers and a rear-seat audio system. LTZ models are further differentiated by a completely different instrument panel and door panels, a huge, 20.1-liter center console storage area, and upgraded five-liter glove box. Ultrasonic rear parking assist is available. Underneath, the carefully engineered hydroformed frame is fully boxed, and has "C" channel sections that combine to make an incredibly stiff backbone. The Sierra is so solid, it feels as if it was carved out of one big block of steel. The work truck and SLE trims are equipped on more of a budget for those who plan to use their pickup for utility, with a more basic interior treatment. These trims have still been upgraded with a new double glove box design, larger control knobs, and a lockable in-seat storage bin that's large enough for a laptop computer and has a built-in 12-volt power outlet. The SLE adds popular equipment such as air conditioning, cruise control, and a CD/MP3 audio system, and a Convenience Package brings more luxury in the way of a remote starting system, adjustable power pedals, and rear park assist. Seating has been improved all around. Stadium-style rear seating, which is split 60/40 and has a fold-down center armrest, is standard on the crew cab and available on the extended cab. Rear legroom on extended cab models is adequate and ingress is now improved thanks to rear access doors that open 170 degrees. Each trim level is available in either 2WD or an on-demand 4WD system with locking rear differential. A 195-horsepower, 4.3L V6 is standard on regular cab and 2WD extended cab Work Truck models, while a 295-horsepower, 4.8L V8 is standard on 4WD extended cab Work Truck models, SLE regular cab and extended cab models, and crew cab Work Truck and SLE models. A 315-horsepower, 5.3L V8 with Active Fuel Management is standard on crew cab SLE2 and all SLT body types. That 5.3L V8 is available as an option on all other models, while there's also a FlexFuel version that adds E85 compatibility. Thanks to Active Fuel Management, the 5.3L gasoline Sierra is rated at 15 city, 20 highway, the same as the base 4.3L V6 and one of the best figures in its class. As part of the trailering package, a 367-horsepower (and 375 ft-lb of torque), 6.0L V8 is available on SLE and SLT extended and crew cab models. This engine has variable valve timing and Active Fuel Management. The package also includes a locking differential, heavy-duty cooling system, and high-capacity air cleaner. Each of the four suspension systems available on the Sierra are tailored for particular driving situations, and each has a completely different character. The Z83 delivers the best ride, while the Z85 upgrades for improved handling and towing capacity. The Z71 is the option for those who plan to take their Sierra off-road, and for those wanting optimized street performance there's the Z60, which rides on 20-inch wheels. Cargo bed lengths are 5'-8" for the short bed, 6'-6" for the standard bed, and 8' for the long bed, and rated payload goes up to 2,160 pounds when properly equipped. The OnStar Generation 7 system is standard on all Sierras, including automatic crash notification and a one-year subscription to the Safe & Sound plan. An ultra-plush GMC Sierra Denali crew cab (in both 2WD and AWD) is available as well. It uses a 6.2L V8 with variable valve timing to produce 403 horsepower and 417 ft-lbs of torque. A six-speed automatic transmission, a locking rear differential, skid plates, StabiliTrak, high-performance suspension, fog lamps, heated mirrors, and rear parking assist are standard, as are a slew of interior luxury items. Optional 20-inch wheels can replace the standard 18-inch alloys.