GMC 2003 GMT560 T-Series Owner's Manual page 137

The heavier the rain, the harder it is to see. Even if your
windshield wiper blades are in good shape, a heavy
rain can make it harder to see road signs and
traffic signals, pavement markings, the edge of the road
and even people walking.
It's wise to keep your wiping equipment in good shape
and keep your windshield washer tank filled with
washer fluid. Replace your windshield wiper inserts
when they show signs of streaking or missing areas on
the windshield, or when strips of rubber start to
separate from the inserts.
Driving too fast through large water puddles or even
going through some vehicle washes can cause
problems, too. The water may affect your brakes. Try to
avoid puddles. But if you can't, try to slow down
before you hit them.
{
CAUTION:
Wet brakes can cause accidents. They won't
work as well in a quick stop and may cause
pulling to one side. You could lose control of
the vehicle.
After driving through a large puddle of water
or a vehicle wash, apply your brake pedal
lightly until your brakes work normally.
4-19