GMC 2011 Sierra Owner's Manual page 323

Never exceed the GVWR for
your vehicle, or the GAWR for
either the front or rear axle.
The Certification/Tire label also
contains important information
about your Front Axle Reserve
Capacity. See What is front axle
reserve capacity, and how do I
calculate it? under
.
In the case of a sudden stop
or collision, things carried in
the bed of your truck could
shift forward and come into
the passenger area, injuring
you and others. If you put
things in the bed of your truck,
you should make sure they
are properly secured.
Do not load the vehicle any
heavier than the Gross
Vehicle Weight Rating
(GVWR), or either the
maximum front or rear Gross
Axle Weight Rating (GAWR).
This can cause systems to
break and change the way the
vehicle handles. This could
cause loss of control and a
crash. Overloading can also
shorten the life of the vehicle.
Using heavier suspension
components to get added
durability might not change
your weight ratings. Ask your
dealer to help you load your
vehicle the right way.