GMC Sierra Denali Classic 2007 Owner's Manual page 107

DRIVE (D): This position is for normal driving. It
provides the best fuel economy for your vehicle. If
you need more power for passing, and you are:
•
Going less than about 35 mph (55 km/h), push
your accelerator pedal about halfway down.
•
Going about 35 mph (55 km/h) or more, push
the accelerator all the way down.
You will shift down to the next gear and have
more power.
Downshifting the transmission in slippery road
conditions could result in skidding, see "Skidding"
under Loss of Control on page 264.
DRIVE (D) can be used when towing a trailer,
carrying a heavy load, driving on steep hills or
for off-road driving. You may want to shift the
transmission to THIRD (3) or, if necessary, a lower
gear selection if the transmission shifts too often.
THIRD (3): This position is also used for normal
driving. It reduces vehicle speed more than
DRIVE (D) without using your brakes. You might
choose THIRD (3) instead of DRIVE (D) when
driving on hilly, winding roads, when towing
a trailer, so there is less shifting between gears
and when going down a steep hill.
SECOND (2): This position reduces vehicle speed
even more than THIRD (3) without using your
brakes. You can use SECOND (2) on hills. It can
help control your speed as you go down steep
mountain roads, but then you would also want to
use your brakes off and on.
If you manually select SECOND (2), the
transmission will drive in second gear. You may
use this feature for reducing the speed of the rear
wheels when you are trying to start your vehicle
from a stop on slippery road surfaces. Once
the vehicle is moving, shift into DRIVE (D). See
Low Traction Mode later in this section.
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