GMC 2005 Sierra Denali Owner's Manual page 264

The trailer tongue weight (A) should be 10 percent to
15 percent of the total loaded trailer weight (B), up to a
maximum or 600 lbs (272 kg) with a weight carrying hitch.
The trailer tongue weight (A) should be 10 percent to
15 percent of the total loaded trailer weight, up to a
maximum of 1,000 lbs (453 kg) with a weight distributing
hitch.
Do not exceed the maximum allowable tongue weight
for your vehicle. Choose the shortest hitch extension
that will position the hitch ball closest to the vehicle. This
will help reduce the effect of trailer tongue weight on
the rear axle.
4-56
After you have loaded the trailer, weigh the trailer and
then the tongue separately, to see if the weights
are proper. If they are not, you may be able to get them
right by moving some items around in the trailer.
Total Weight on Your Vehicle's Tires
Be sure your vehicle's tires are inflated to the upper limit
for cold tires. You'll find these numbers on the
Certification label at the rear edge of the driver's door or
see Loading Your Vehicle for more information. Then
be sure you don't go over the GVW limit for your vehicle,
or the GAWR, including the weight of the trailer
tongue. If you use a weight distributing hitch, make sure
you don't go over the rear axle limit before you apply
the weight distribution spring bars.
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.