GMC Sierra 2000 Owner's Manual page 322

Inflation -- Tire Pressure
The Certification/Tire label, which is on the rear edge of
the driver's door, or on the incomplete vehicle document
in the cab, shows the correct inflation pressures for your
tires when they're cold. "Cold" means your vehicle has
been sitting for at least three hours or driven no more
than 1 mile (1.6 km).
NOTICE:
Don't let anyone tell you that underinflation or
overinflation is all right. It's not. If your tires
don't have enough air (underinflation), you can
get the following:
D
Too much flexing
D
Too much heat
D
Tire overloading
D
Bad wear
D
Bad handling
D
Bad fuel economy.
6-50
NOTICE: (Continued)
NOTICE: (Continued)
If your tires have too much air (overinflation),
you can get the following:
D
Unusual wear
D
Bad handling
D
Rough ride
D
Needless damage from road hazards.
When to Check
Check your tires once a month or more. Also, check
the tire pressure of the spare tire.
How to Check
Use a good quality pocket
pressure. You can't tell if your tires are properly inflated
simply by looking at them. Radial tires may look
properly inflated even when they're underinflated.
Be sure to put the valve caps back on the valve stems.
They help prevent leaks by keeping out dirt and moisture.
-
type gage to check tire