GMC Sierra Denali Owner's Manual page 133

Cruise Control
0
:
off
I
:
On
t
: Resume/Accelerate
R :
Set
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).
If you apply your brakes, or press the clutch pedal (if
equipped), the cruise control will disengage.
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.
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.
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