GMC Hummer H3 2008 Owner's Handbook Manual page 237

Starting and Operating Instructions
NOTICE
Pulling a trailer improperly can
damage your vehicle and result
in costly repairs not covered by
your warranty. To pull a trailer
correctly, follow the advice in
this section.
If you think you want to pull a
trailer, see your dealer for infor-
mation on your vehicle's trailer
towing ability.
. . . 236
The maximum loaded trailer
weight you can pull with your
vehicle depends on your intended
use and what special equipment
has been installed on the vehicle.
Information on trailer towing abili-
ty, special equipment required,
and optional equipment available
should be obtained from your
dealer. Installation of towing
equipment should be carried out
only by your dealer. Your dealer
has the proper installation specifi-
cations and is aware of any neces-
sary vehicle modifications.
Maximum trailer weight is calcu-
lated assuming only the driver is in
the tow vehicle and it has all the
required trailering equipment. The
weight of additional optional
equipment, passengers and cargo
in the tow vehicle must be
subtracted from the maximum
trailer weight.