2007 GMC Sierra 1500 Pickup Owner's Manual - Page 167

Shifting from Four-Wheel Drive Low to Four-Wheel Drive High or Two-Wheel Drive High To shift from Four-Wheel Drive Low to Four-Wheel Drive High or Two-Wheel Drive High, your vehicle must be stopped or moving less than 3 mph (5 km/h) with the transmission in NEUTRAL (N) for an automatic transmission or the clutch pedal pressed for a manual transmission. The preferred method for shifting out of Four-Wheel Drive Low is to have your vehicle moving 3 mph (5 km/h). Press and release the Two-Wheel Drive High or Four-Wheel Drive High switch. You must wait for the Two-Wheel Drive High or Four-Wheel Drive High indicator light to stop flashing and stay on before shifting the transmission into gear or releasing the clutch pedal. If the Four-Wheel Drive High switch is pressed when your vehicle is in gear, the Four-Wheel Drive High indicator light will flash for 30 seconds but the vehicle will not complete the shift unless it is moving slower than 3 mph (5 km/h) and the transmission is in NEUTRAL (N). Shifting into NEUTRAL {CAUTION: Shifting the transfer case to NEUTRAL can cause your vehicle to roll even if the transmission is in PARK (P). You or someone else could be seriously injured. Be sure to set the parking brake before placing the transfer case in NEUTRAL. See Parking Brake on page 169. To shift the transfer case to NEUTRAL, first make sure the vehicle is parked so that it will not roll: 1. Set the parking brake and apply the regular brake pedal. 2. Start the vehicle or turn the ignition to RUN. 3. Press the foot brake pedal and put the transmission in NEUTRAL (N). 4. Shift the transfer case to Two-Wheel Drive High. 167