Sharing the spotlight with these engines are heavy-duty transmissions, specially engineered to handle tremendous torque. Mo. When descending a hill, vehicle speed, load weight and deceleration rate are monitored, and Engine Grade Braking automatically shifts to a lower gear to slow the truck. Pressing the Tow-Haul mode button accomplishes a similar mission, reducing speed by steady, progressive downshifting. Tow-haul mode also lessens shift confusion on uphill climbs, eliminating gear hunting by holding the optimum gear. First gear is the granny type, with usefulness limited to getting heavy loads into motion.
Second gear is the launcher for unloaded trucks.
An optional four-speed automatic adjusts engine torque, offering smooth gear transitions. These capable powertrains are cradled in modular multisectional frames that are lighter but stronger than past-generation frames. These precise frames lessen twisting, bending and vibrations, allowing engineers greater control over suspension tuning. GM gives chassis integrity a 200,000-mile rating at a brutal 98 percentile severity level. Bodies perched atop these more capable frames also benefit from improved designing.