GMC 2000 Safari Owner's Manual page 98

DRIVE (D): This position is for normal driving.
If you need more power for passing, and you're:
D
Going less than about 35 mph (55 km/h),
push your accelerator pedal about halfway down.
D
Going about 35 mph (55 km/h) or more, push
the accelerator pedal all the way down. You'll shift
down to the next gear and have more power.
DRIVE (D) should be used for normal towing.
THIRD (3): This position is also used for normal
driving, however it offers more power and lower fuel
economy than DRIVE (D). You should use THIRD (3)
when carrying a heavy load or driving on steep hills.
SECOND (2): This position gives you more power but
lower fuel economy. 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 torque to the rear wheels when you are
trying to start your vehicle from a stop on slippery
road surfaces.
FIRST (1): This position gives you even more power
(but lower fuel economy) than SECOND (2). You
can use it on very steep hills, or in deep snow or mud.
If the selector lever is put in FIRST (1), the transmission
won't shift into first gear until the vehicle is going
slow enough.
NOTICE:
If your rear wheels can't rotate, don't try to drive.
This might happen if you were stuck in very deep
sand or mud or were up against a solid object.
You could damage your transmission or transfer
case or both.
Also, if you stop when going uphill, don't hold
your vehicle there with only the accelerator pedal.
This could overheat and damage the transmission.
Use your brakes or shift into PARK (P) to hold
your vehicle in position on a hill.
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