GMC 2011 Sierra Owner's Manual page 406

It is important that the combination
of the tow vehicle and trailer
does not exceed any of its weight
ratings GCWR, GVWR, RGAWR,
Trailer Weight Rating, or Tongue
Weight. The only way to be sure it is
not exceeding any of these ratings
is to weigh the tow vehicle and
trailer combination, fully loaded for
the trip, getting individual weights
for each of these items.
The correct hitch equipment helps
maintain combination control.
Most small-to-medium trailers can
be towed with a weight-carrying
hitch which simply features a
coupler latched to the hitch ball.
Larger trailers may require a
weight-distributing hitch that
uses spring bars to distribute
the trailer tongue weight among
the two vehicle and trailer axles.
Fifth-wheel and gooseneck hitches
may also be used. See Weight of
the Trailer Tongue under
for rating
limits with various hitch types.
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.
Consider using sway controls
with any trailer. Ask a trailering
professional about sway controls
or refer to the trailer manufacturer's
recommendations and instructions.
A. Body to Ground Distance
B. Front of Vehicle
When using a weight-distributing
hitch, the spring bars should be
adjusted so the distance (A) is the
same after coupling the trailer to the
tow vehicle and adjusting the hitch.