GMC Sierra 2000 Owner's Manual page 324

When you install dual wheels, be sure the vent holes in
the inner and outer wheels on each side are lined up.
After the tires have been rotated, adjust the front and rear
inflation pressures as shown on the Certification/Tire label.
Make certain that all wheel nuts are properly tightened.
See "Wheel Nut Torque" in the Index.
6-52
If your vehicle has dual rear
wheels and the load range
or tread design for your
front tires is different from
your rear tires, always use
the correct rotation pattern
shown here when rotating
your tires. The dual tires
are rotated as a pair, and
the inside rear tires become
the outside rear tires.
CAUTION:
Rust or dirt on a wheel, or on the parts to which
it is fastened, can make wheel nuts become loose
after a time. The wheel could come off and cause
an accident. When you change a wheel, remove
any rust or dirt from places where the wheel
attaches to the vehicle. In an emergency, you
can use a cloth or a paper towel to do this; but
be sure to use a scraper or wire brush later,
if you need to, to get all the rust or dirt off.
(See "Changing a Flat Tire" in the Index.)