GMC 2009 Sierra 1500 Crew Cab Owner's Manual page 518

5. If the spare does not lower, turn the wrench
counterclockwise until approximately 6 inches
(15 cm) of cable is exposed.
6. Stand the wheel blocks on their shortest ends, with
the backs facing each other.
5-108
7. Place the bottom
edge of the jack (A)
on the wheel blocks (B),
separating them so that
the jack is balanced
securely.
8. Attach the jack handle, extension, and wheel
wrench to the jack and place it (with the wheel
blocks) under the vehicle toward the front of the
rear bumper.