2005 GMC Sierra 1500 Pickup Owner's Manual - Page 493

If you have added a snow plow to the front of your vehicle, lower the snow plow fully before raising the vehicle. {CAUTION: Getting under a vehicle when it is jacked up is dangerous. If the vehicle slips off the jack you could be badly injured or killed. Never get under a vehicle when it is supported only by a jack. Jacking Locations A. Front Location (Two-Wheel-Drive 1500 Series) B. Front Location (All Other Series) C. Rear Location (All Series) 3. Position the jack under the vehicle as shown. If the flat tire is on the front of the vehicle (two-wheel-drive 1500 Series vehicles), position the jack under the bracket attached to the vehicle's frame, behind the flat tire. If the flat tire is on the front of the vehicle (all other models), position the jack on the frame behind the flat tire. If the flat tire is on the rear, position the jack under the rear axle between the spring anchor and the shock absorber bracket. {CAUTION: Raising your vehicle with the jack improperly positioned can damage the vehicle and even make the vehicle fall. To help avoid personal injury and vehicle damage, be sure to fit the jack lift head into the proper location before raising the vehicle. 5-99