1990 Plymouth Voyager Repair Question
Staying in second gear is called "limp mode" that allows you to drive slowly to a repair shop without needing a tow truck.
In general, when it starts out in second gear without going through an up-shift, it's usually a speed sensor or other electrical problem. When it doesn't go back to second gear until or during an up-shift, that is usually caused by slippage of a clutch pack and will lead to the need to a rebuild.
There WILL be at least one diagnostic fault code stored in the Transmission Computer. An experienced transmission mechanic will know how to proceed after reading those codes.
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