GMC 2009 Sierra 1500 Crew Cab Owner's Manual page 512

Front Position - 1500
Models
4. Position the jack under the vehicle as shown. If the
flat tire is on the front of the vehicle (1500 Model
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.
5-102
Front Position - All
Other Models
Rear Position – 1500
Models
If the flat tire is on the rear, for 1500 models
position the jack under the rear axle about
2 inches (5 cm) inboard of the shock absorber
bracket; for all other models, position the jack
under the rear axle between the spring anchor
and the shock absorber bracket.
If you have added a snow plow to the front of your
vehicle, lower the snow plow fully before raising
the vehicle.
Make sure that the jack head is positioned so
that the rear axle is resting securely between the
grooves that are on the jack head.
Rear Position – All
Other Models