GMC 2008 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.
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.
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.
Front Position
5-87