GMC 2009 Sierra 1500 Crew Cab Owner's Manual page 393

Hitches
It is important to have the correct hitch equipment.
Crosswinds, large trucks going by and rough roads are
a few reasons why the right hitch is needed.
Weight-Distributing Hitches and Weight
Carrying Hitches
A: Body to Ground Distance
B: Front of Vehicle
When using a weight-distributing hitch, the hitch must
be adjusted so the distance (A) remains the same both
before and after coupling the trailer to the tow vehicle.
If a step-bumper hitch will be used, the bumper could be
damaged in sharp turns. Make sure there is ample
room when turning to avoid contact between the trailer
and the bumper.
If the loaded trailer being pulled will weigh more than
5,000 lbs (2 270 kg), be sure to use a properly mounted
weight-distributing hitch and sway control of the proper
size. This equipment is very important for proper vehicle
loading and good handling when driving. Always use a
sway control if the trailer will weigh more than these
limits. Ask a hitch dealer about sway controls.
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