The 2015 GMC Sierra is offered in Regular Cab, Double Cab (extended cab) and Crew Cab models, with two different bed lengths. Among those, power is provided by a choice between V6 and V8 powertrains. The base 4.3L V6 makes 285 horsepower and 305 pound-feet of torque, while the available EcoTec3 5.3L V8 makes 355 horsepower and 383 pound-feet. Both the 4.3L and 5.3L engines are certified to run on E85 (an 85-percent ethanol blend). Separately, at the top of the line, a 6.2L EcoTec3 V8 is positioned for those who regularly tow or haul the heaviest loads. This engine is only offered in Double Cab and Crew Cab models and makes 420 horsepower and 460 pound-feet of torque. With the V6 or 5.3 V8, the transmission is a 6-speed automatic, while the 6.2L V8 is paired with a new 8-speed automatic adapted from the Corvette. Both provide a tall cruising gear for good highway mileage (there are three axle ratios from which to choose). In addition, all three engines are aluminum-alloy, featuring variable valve timing and direct injection, as well as Active Fuel Management that allows them to run on four cylinders during light-load conditions like cruising and coasting. V6 models have fuel economy ratings of up to 18 mpg city, 24 highway with rear-wheel drive. The combination of three cab styles and two bed lengths can cover quite a range of wheelbases, which range from 119 inches all the way up to 153 inches. Front and rear Park Assist is available -- helpful for those who use their trucks in daily urban or suburban driving. Forward Collision Alert and Lane Departure Warning are among the active-safety features offered in the 2015 Sierra, and in both cases they might help avoid an accident from happening altogether. Inside, the Sierra has a traditional, upright instrument panel layout, with soft-touch materials and superb attention to detail. Knobs and buttons are large enough to use with gloves on, and there are two glovebox compartments. Double Cab models include rear-hinged front doors, with enough of a back seat for most passengers, while Crew Cab models offer a full, SUV-sized backseat. Depending on the trim level, the Sierra includes up to five USB outlets, four 12-volt outlets, an SD card slot, and an AC outlet -- with the available IntelliLink infotainment system wrapping in an 8-inch touch screen for compatibility with Bluetooth calling and streaming audio features, as well as Pandora streaming audio. The latest generation of OnStar is available, as well as 4G LTE WiFi capability, which turns the Sierra into a hotspot. Integral LED bed lighting, movable upper tie-downs, bumper-corner steps, and a damped, EZ Lift and Lower tailgate are just a few of the cargo-box innovations in the Sierra. An available spray-on bed liner helps protect it, too. Several specialty models cater to the needs of certain kinds of truck users. For instance, a Sierra All-Terrain model includes a look with less chrome, a painted grille, and serious off-road equipment such as monotube Rancho shocks, a transfer-case shield, hill descent control, front recovery hooks, and an automatic locking rear differential to help in mud or snow. Even at the base level, the Sierra includes a 40/20/40-split bench seat, power locks, cruise control, air conditioning, a tilt-adjustable steering column, and an audio system with USB ports, an SD card slot, and a 4.2-inch color display. At the top of the lineup, the Sierra Denali offers its own unique look, as well as a "loaded" array of features and comfort items. A chrome grille, special 20-inch chrome wheels and polished stainless steel exhaust -- plus body-color bumpers and special trim -- set a more elegant look on the outside. Inside the Denali gets real aluminum trim, bright door sills and upgraded trim. Meanwhile, the long list of feature upgrades for this model includes a navigation system with Intellilink, five USB ports, Bose audio, heated and cooled leather front seats, a heated steering wheel, a power-sliding rear window and front and rear park assist.