Overview

What Changed for 2008:

• XM satellite radio standard on all models


• 17-inch wheels standard on dual-rear-wheel (DRW) models


• Power-adjustable driver's seat available with regular cab's bench seat

Overview
GMC, which has been in the heavy-duty pickup truck market for decades, most recently redesigned its Sierra HD (Heavy Duty) pickups for the 2007 model year. Sierra HD trucks come in two models: three-quarter-ton 2500HD and 3500HD. Both models offer 6-foot-6-inch or 8-foot bed lengths and a choice of three cab designs: regular cab, extended cab, and crew cab. Extended cabs and crew cabs have 4 doors and seat 6 with a folding second-row bench seat; it is split in crew cabs and a split rear seat is optional in extended cabs. The extended cab's rear access doors open 170 degrees and don't open independently of the front doors. The crew cab has full-size rear doors. Sierra 3500HD models with the long bed are available in a DRW configuration. Rear-wheel drive (RWD) and 4-wheel drive (4WD) are offered for all models.

Model Lineup
Four trim levels are offered on the 2008 GMC Sierra HD: Work, SLE1, SLE2 and SLT. All but SLT have GM's "pure pickup" interior design with larger controls, a double glovebox, a fold-down armrest storage console, and a lockable underseat center storage bin with a power outlet. The SLT has a "luxury-inspired" design with smaller controls, a single glove box, and more upscale trim.

Standard equipment on the Work trim level consists of an AM/FM/CD stereo; XM satellite radio with 3-month subscription; driver information center; vinyl floor covering; one year of OnStar service; vinyl upholstery; a 40/20/40-split front bench seat; GM's Z85 handling/trailering suspension; and 16-inch steel wheels for the 2500HD and 17-inch steel wheels for the 3500HD. Extended and crew cab 2500HD models also have air conditioning. The SLE1 trim includes cruise control; leather-wrapped steering wheel; power, heated outside mirrors; power windows and door locks; remote keyless entry; auto-dimming rearview mirror; cloth upholstery; and chromed steel wheels. The 3500HD SLE1 also has fog lights. SLE2 trim includes dual-zone automatic climate control; 6-way power-adjustable front bucket seats; front center console; and steering wheel audio controls. The SLT trim adds Bose speakers with a subwoofer; leather upholstery; heated, 12-way power front seats; driver's seat memory; and 17-inch aluminum wheels.

Options on the 2008 GMC Sierra HD include a sunroof; power-adjustable pedals; remote engine starting; universal garage door opener; auxiliary battery; 6-disc CD changer; locking rear differential; integrated trailer-brake controller; heavy-duty towing package; skid plate package; GM's Z71 off-road suspension; DVD-based navigation system; and a rear DVD entertainment system. An available cargo management system for the bed has aluminum front and side C-channels with upper and lower tracks and four adjustable tie-down hooks.

Powertrain
The base engine in the 2008 GMC Sierra HD is GM's Vortec 6.0-liter V-8, which makes 353 hp at 5400 rpm and 373 lb.-ft. of torque at 4400 rpm. It is mated to a 6-speed automatic transmission with two overdrive gears and manual-shift capability. Also offered is the Duramax Turbo Diesel 6.6-liter V-8 engine, which produces 365 hp at 3200 rpm and 660 lb.-ft. of torque at 1600 rpm. It comes with an Allison 1000 6-speed automatic transmission that features what GM touts to be a class-first range-selection function.

The standard 4WD setup is a part-time system that should not be left engaged on dry pavement and has low-range gearing. Also offered is GM's AutoTrac 4WD, which can be left engaged on dry pavement and includes low-range gearing. A Sierra 2500HD can haul a maximum payload of 3892 pounds, while a 3500HD can handle up to 5307 pounds of payload. Both can tow up to 13,000 pounds, and the DRW 3500HD can tow up to 16,700 pounds when equipped with a fifth-wheel hitch.

Safety
Standard safety equipment on the 2008 GMC Sierra HD includes dual front air bags, anti-lock (ABS) 4-wheel disc brakes, and a tire-pressure monitor. Rear obstacle detection is optional. The GMC Sierra 2500HD and 3500HD have not been crash tested by the National Highway Traffic Safety Administration (NHTSA) or the Insurance Institute for Highway Safety (IIHS).

Technology
The integrated trailer-brake controller on the 2008 GMC Sierra HD is located on the instrument panel and precludes the need for external or aftermarket brake control systems, GMC says. The trailer-brake controller is integrated with the ABS system and provides immediate and measured brake-force signaling to electric-controlled trailer brake systems, the automaker adds.