92 caravan

its a 92 caravan with 180000 miles 3.1 v-6. the motor runs great. then the transmission just went into limp mode pretty much out of nowhere. Shouldnt it show signs of failing ie slipping and so forth? I was reading a post earlier and saw something about a speed sensor could cause this problem? The van is parked and has been for a while. I lost hope because i assumed it needed a new transmission which it may but if this sensor is causing the problem that would be great news. Either that or.....anybody got a working transmission for a 92 caravan for sale? Id like to at least sell it and get something out of it. The interior is in perfect shape. The paint is peeling off however. And like i said it runs great. Any suggestions?

Could also be Transmission Control Module.
Our 91 suddenly went into limp mode one day while driving at highway speeds. i bought the computer at a local salvage yard off a 93, and have been driving it trouble free (tranny wise) ever since.
Hope this helps and good luck!