GMC 2014 Sierra Owner's Manual page 273

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
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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 the
weight ratings. Ask your dealer
to help load the vehicle the
right way.
If you put things inside the
vehicle like suitcases, tools,
packages, or anything
else they go as fast as the
vehicle goes. If you have to stop
or turn quickly, or if there is a
crash, they will keep going.
Things you put inside the
vehicle can strike and injure
people in a sudden stop or
turn, or in a crash.
Put things in the cargo
area of the vehicle. Try to
spread the weight evenly.
Never stack heavier
things, like suitcases,
inside the vehicle so that
some of them are above
the tops of the seats.
Do not leave an
unsecured child restraint
in the vehicle.
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