anyone know these transmissions?

I have a 90 plymouth voyager that doesn't want to shift out of first a lot (now), and when I turn it off and back on, it fixes it most of the time. I've been asking all over town and the internet and have gotten a range of answers.
One person has told me that it's a tranny computer problem and I can simply reset it where it is hooked into the battery. First question: is this feasible, because if the computer is acting up, then, won't it still be when I reconnect it? My problem is solved almost each time I turn the van off and back on again, which has been a temporary solution to my problem at this point.
One person says I need to get the diagnostics first, so my second questions is what does CVI stand for and how can I use these if I don't trust the mechanic?
Also, if this tranny computer resets when I turn it off, then, how will a diagnostic help?
One person says, it could be my speed sensor, so will a diagnostic tell me that this sensor doesn't work?

rmc, please check out my post in the Chrysler Town and Country Forum your problem sound just like what my 96 T & C was doing, but by no means take it to Aamco that was a total waste of $89.00. It may be the sensors there 2 on mine that they replaced.
digimon

It cost me 30 bucks to have a tranny joint plug a computor into the cars computor which told us it was an internal problem. If your car (not sure about 90's) has a diagnostic plug, take it to them and have them see what the computor is telling them. Any tranny joints have these tools.

Mine has been shifting just fine since I had the speed sensers replaced. Ride On, digimon