Ford 1999 F-350 Owner's Manual page 122

Driving
2. Set parking brake.
3. Shift into 1 (First).
4. Turn the ignition key to position
3 (OFF).
Do not park your vehicle in Neutral, it may move unexpectedly
and injure someone. Use 1 (First) gear and set the parking brake
fully.
Reverse
Make sure that your vehicle is at a complete stop before you shift into
R (Reverse). Failure to do so may damage the transmission.
Put the gearshift in N (Neutral) and wait at least three seconds before
shifting into R (Reverse).
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