Ford Probe Owner's Manual page 151

When to use Drive (D with Overdrive OFF)
In Drive (Overdrive OFF), your vehicle
automatically upshifts or downshifts from 1st
through 4th gears as the vehicle speeds up or
slows down. It also downshifts when you need
extra acceleration to pass or when driving up a
hill.
Selecting Drive (Overdrive OFF) will eliminate
the transaxle's tendency to "hunt" between third
and fourth gears while driving over hilly terrain.
It also gives your vehicle more engine braking to
slow your vehicle than Overdrive does.
When to use Second (2)
Use Second (2) to help drive up moderately
steep hills or when starting on slick surfaces. It
prevents the transaxle from frequently shifting
up and down. It also gives more engine braking
than Overdrive or Drive when going down hills.
Do not go faster than 64 mph (102 km/h) with
the gearshift in the Second (2) position. If you
shift from Overdrive or Drive to Second because
of hilly terrain, your transaxle will automatically
downshift in the proper sequence.
When to use First (1)
When your vehicle is in First (1), it gives more
engine braking to slow your car than Drive (D
with Overdrive OFF) on downgrades.
Do not go faster than 32 mph (50 km/h) in this
gear. You can upshift from First (1) into D
Position at any speed. If you shift from
Overdrive or Drive to First (1) because of hilly
terrain, your transaxle will automatically
downshift in the proper sequence.
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