Chevrolet 2008 Express Owner's Manual page 240

Hitches
It's important to have the correct hitch equipment.
Crosswinds, large trucks going by and rough roads are
a few reasons why you'll need the right hitch.
The rear bumper on your vehicle is not intended for
hitches. Do not attach rental hitches or other
bumper-type hitches to it. Use only a frame-mounted
hitch that does not attach to the bumper.
4-36
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 that the distance (A) remains the
same both before and after coupling the trailer to the
tow vehicle.
If you use a step-bumper hitch, your bumper could be
damaged in sharp turns. Make sure you have ample
room when turning to avoid contact between the trailer
and the bumper.