GMC 2007 Sierra 1500 Pickup Owner's Manual page 42

3. Be sure that the belt is not twisted and it lies
flat. The elastic cord must be under the belt
and the guide on top.
42
CAUTION:
{
A safety belt that is not properly worn
may not provide the protection needed in
a crash. The person wearing the belt
could be seriously injured. The shoulder
belt should go over the shoulder and
across the chest. These parts of the body
are best able to take belt restraining
forces.