GMC Sierra 2000 Owner's Manual page 108

Cruise Control (If Equipped)
When you apply your brakes, the cruise control
shuts off.
2-40
With cruise control, you can
maintain a speed of about
25 mph (40 km/h) or more
without keeping your foot
on the accelerator. This can
really help on long trips.
Cruise control does not
work at speeds below about
25 mph (40 km/h).
CAUTION:
D
Cruise control can be dangerous where you
can't drive safely at a steady speed. So,
don't use your cruise control on winding
roads or in heavy traffic.
D
Cruise control can be dangerous on
slippery roads. On such roads, fast changes
in tire traction can cause needless wheel
spinning, and you could lose control. Don't
use cruise control on slippery roads.