2001 GMC Sierra 1500 Pickup Owner's Manual - Page 119

You can shift from 2-Wheel High (2HI) to 4-Wheel High (4HI) or from 4-Wheel High (4HI) to 2-Wheel High (2HI) while the vehicle is moving. Your front axle will engage faster if you take your foot off of the accelerator for a couple of seconds after you shift. In extremely cold weather, it may be necessary to stop or slow the vehicle to shift into 4-Wheel High (4HI). To shift into or out of 4-Wheel Low (4LO) or NEUTRAL (N): 1. Slow the vehicle to a roll, about 1 to 3 mph (2 to 5 km/h) and shift an automatic transmission into NEUTRAL (N), or with a manual transmission, press the clutch pedal. 2. Shift the transfer case shift lever in one continuous motion. Don't pause in NEUTRAL (N) as you shift the transfer case into 4-Wheel Low (4LO), or your gears could clash. Remember that driving in 4-Wheel High (4HI) or 4-Wheel Low (4LO) may reduce fuel economy. Also, driving in four-wheel drive on dry pavement could cause your tires to wear faster and make your transfer case harder to shift and run noisier. Automatic Transfer Case (If Equipped) The transfer case switches are located to the left of the instrument panel cluster. Use these switches to shift into and out of four-wheel drive. 2-36