Transmission will not shift out second gear

Second gear is limp mode that allows you to drive slowly to a repair shop without needing a tow truck. You can get an idea of the type of cause if you observe when it defaults to limp mode. Is it during or right after an up-shift? That would be typical of a slipping clutch pack. You'll need to stop the engine and restart it to get it out of limp mode, then it may shift normally again for days or weeks. If it goes into limp mode the instant you shift out of "park", it is more likely to be sensor or electrical-related.

Regardless of the cause, there will be diagnostic fault codes in the Transmission Computer. You'll need to find a mechanic with a scanner that can access that computer to read those codes.

This article:

https://www.2carpros.com/articles/retrieve-trouble-codes-for-chrysler-dodge-plymouth-odb1-1995-and-earlier-car-mini-van-and-light-trucks

shows how to read fault codes in the Engine Computer yourself with no special tools. Chrysler made doing that much easier than any other manufacturer.

This article:

https://www.2carpros.com/articles/automatic-transmission-problems

shows some of the things we look for during the diagnosis.