We have an 2003 F-150 4x4 FX4 that won't go forward, but when we push it up to 30kph it drives and shifts fine?
Sounds like the transmission has a problem. have a tranny specialist check it out.
Sounds like the torque converter is shot.
Is the o/d light on the dash flashing?
It is probably not going down into first or first is slipping bad. Or worse there is a trans fault and it is defaulting to 3rd. You need it to get checked out by a trans shop. Chances are the torque converter was able to compensate for this but it too may have gone out due to being over worked
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