2008 GMC Sierra 1500 Pickup Owner's Manual - Page 399

{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. 4. Position the jack under the vehicle. If the flat tire is on the front of the vehicle, 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. Front Position 5-87