2012 GMC Sierra Owner's Manual - Page 316

9-40 Driving and Operating the Range Selection Mode. Grade Braking assists in maintaining desired vehicle speeds when driving on downhill grades by automatically implementing a shift schedule that utilizes the engine and transmission to slow the vehicle. This reduces wear on the braking system and increases control of the vehicle. Grade Braking monitors vehicle speed, acceleration, engine torque and brake pedal usage. Using this information, it detects when the truck is on a downhill grade and the driver desires to slow the vehicle by pressing the brake. This feature is active when the exhaust brake is enabled (if equipped). Also see Towing Equipment on page 9‑94 for more information. See Tow/Haul Mode Light on page 5‑26 and Hill and Mountain Roads on page 9‑12 for more information. Also see "Tow/Haul Mode" under Towing Equipment on page 9‑94 for more information. Drive Systems Four-Wheel Drive If the vehicle has Four-Wheel Drive, you can send the engine's driving power to all four wheels for extra traction. To get the most satisfaction out of Four-Wheel Drive, you must be familiar with its operation. Read the following before using Four-Wheel Drive. See the appropriate text for the transfer case in the vehicle. Notice: Driving on clean, dry pavement in Four-Wheel Drive High or Four-Wheel Drive Low for an extended period of time may cause premature wear on the vehicle's powertrain. Do not drive on clean, dry pavement in Four-Wheel Drive High or Four-Wheel Drive Low for extended periods of time. Grade Braking (6-Speed Automatic Transmission) The Grade Braking shift modes can be activated by pressing the button on the end of the shift control lever. While in Range Selection Mode, Grade Braking is deactivated allowing the driver to select a desired range of gears. Grade Braking is only active while the Tow/Haul Mode is selected and you are not in the Range Selection Mode. See "Tow/Haul Mode" listed previously and Manual Mode on page 9‑38 for more information on