2003 GMC Yukon Owner's Manual - Page 117

{CAUTION: It is dangerous to get out of your vehicle if the shift lever is not fully in PARK (P) with the parking brake firmly set. Your vehicle can roll. Do not leave your vehicle when the engine is running unless you have to. If you have left the engine running, the vehicle can move suddenly. You or others could be injured. To be sure your vehicle will not move, even when you are on fairly level ground, always set your parking brake and move the shift lever to PARK (P). See "Shifting Into Park (P)" in the Index. If you are pulling a trailer, see "Towing a Trailer" in the Index. {CAUTION: If you have four-wheel drive, your vehicle will be free to roll - even if your shift lever is in PARK (P) - if your transfer case is in NEUTRAL. So, be sure the transfer case is in a drive gear, two-wheel high (2H) or four-wheel high (4H) or four-wheel low (4L) - not in NEUTRAL. See "Shifting into Park (P)" in the index. REVERSE (R): Use this gear to back up. Notice: Shifting to REVERSE (R) while your vehicle is moving forward could damage the transmission. The repairs would not be covered by your warranty. Shift to REVERSE (R) only after your vehicle is stopped. To rock your vehicle back and forth to get out of snow, ice or sand without damaging your transmission, see If You Are Stuck: In Sand, Mud, Ice or Snow on page 4-52. 2-23