2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 180

When Using the Manual Transfer Case . Shifting should be made using quick motions. Shifting slowly may make it more difficult to shift. You may notice that it is harder to shift when the vehicle is cold. After the vehicle warms up the shifting will return to normal. While in Four-Wheel High or Four-Wheel-Drive Low you may experience reduced fuel economy. Avoid driving in Four-Wheel Drive on clean, dry pavement. It may cause your tires to wear faster, make the transfer case harder to shift, and run noisier. If the transfer case shifter is in the N (Neutral) position and you have difficulty reaching the selected transfer case mode, with the engine running, shift the transmission momentarily to drive and then back to N (Neutral). This will realign the gear teeth in the transfer case and allow you to complete the shift. Shifting from Two-Wheel-Drive High to Four-Wheel-Drive High . . Shifts between Two-Wheel-Drive High and Four-Wheel-Drive High can be made at any vehicle speed. Shift the transfer case lever in one continuous motion into either the Four-Wheel-Drive High or Two-Wheel-Drive High position. In extremely cold weather, it may be necessary to slow or stop the vehicle to shift into Four-Wheel-Drive High until the vehicle has warmed up. While in Four-Wheel-Drive High, the vehicle can be driven at any posted legal speed limit. . . . . . . 3-42