GMC 2010 Sierra 1500 Crew Cab Owner's Manual page 444

Fifth wheel and gooseneck trailers can be used
with many pickup models. These trailers place a
larger percentage of the weight (kingpin weight) on the
tow vehicle than conventional trailers. Make sure this
weight does not cause the vehicle to exceed GAWR
or GVWR.
Fifth wheel or gooseneck kingpin weight should be
15 to 25 percent of the trailer weight up to the maximum
amount specified in the trailering chart for the vehicle.
See Weight of the Trailer in this section for more
information.
The hitch should be located in the pickup bed so that its
centerline is over or slightly in front of the rear axle.
Take care that it is not so far forward that it will contact
the back of the cab in sharp turns. This is especially
important for short box pickups. Trailer pin box
extensions and sliding fifth wheel hitch assemblies can
help this condition. There should be at least six inches
of clearance between the top of the pickup box and the
bottom of the trailer shelf that extends over the box.
Make sure the hitch is attached to the tow vehicle frame
rails. Do not use the pickup box for support.
5-68
Always attach chains between the vehicle and the
trailer. Cross the safety chains under the tongue of the
trailer to help prevent the tongue from contacting the
road if it becomes separated from the hitch. Instructions
about safety chains may be provided by the hitch
manufacturer or by the trailer manufacturer. If the trailer
being towed weighs up to 5,000 lbs (2 271 kg) with a
factory-installed step bumper, safety chains may be
attached to the attaching points on the bumper,
otherwise, safety chains should be attached to holes on
the trailer hitch platform. Always leave just enough
slack so the combination can turn. Never allow safety
chains to drag on the ground.
Pressing this button at
the end of the shift lever
turns on and off the
tow/haul mode.