I was thinking maybe a TRS (trans range sensor) but if it was actually stuck in fourth gear it's most likely a little deeper in the trans. All chrsyler transmission use solenoid packs, its what actually controls the shifting of the trans instead of a overly complicated valve body like in the old days. Chrysler transmissions are notorious for bad solenoid packs, i can't even count how many I've replaced at work. Sounds like you either have a bad solenoid or bad wiring for the solenoid pack. Either way it should have a code stored.
Chrysler Dealership Engine, Trans, Axle "Heavy" Tech of 3 years
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