GMC 2010 Yukon/Yukon XL Owner's Manual page 417

Body to Ground Distance
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.
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.
5-55