GMC 2007 Sierra - Manual (Page 373)

If you think you will need some more ground
clearance at the front of your vehicle, you
can remove the front bumper lower air dam.
The front bumper lower air dam is held in place
by a series of push-pins located around the lower
edge of the front bumper. The push-pins are
accessible from underneath the front bumper.
The following steps must be performed on each of
the push-pins to remove the air dam:
1. Insert a tool into the
push-pin slot and
pull downward
until the push-pin
snaps loose.
373