91 Grand Caravan with tranny problems

I have a 91 Caravan. The problem started with the speedodomoter started acting funny. It would bounce all over the place and sometimes just get stuck expecially after going 45 or 50 the needle would just stay on 45 or 50. At first I would just hit the top of the dash and it would kick it back in again and all would be fine for awhile. Then the van started going into limp mode. At first I could just pull over shut the van down for a few minutes and than it would run just fine. Now it just stsays in limp mode. We have found that if we disconnect the battery for a few minutes the van shifts just beautifully, smooth as butter, not limp mode or anything until I slow down to stop the van and then it just pops into limp mode again. Called the dealer and they said to change out the input and output sensors, we did this and still haveing the same problems. I have been reading this forum and found that there is a splice that I can check that there is a Transmission Control Module on the passenger sidewall that may be bad, can anyone tell me what this looks like or where I can find a picture of said part? Also there is a splice point somewhere on the TCM that may be corrorded. Does anyone know where this splice is located? I went ahead and ordered a manual but will take about a week to get here. I need my van as it is my only form of transportation. Also there is also a ground strap on the transmission that may need to be cleaned any ideas where this is located? Also the only error code I'm getting is the 55 end of code thing. Also when the trans does shift it works really really great so I'm pretty sure it's not inside the tranny that is giving me the problem. This is also kinda strange to, last night after replacing both the sensors my son went with me to test drive when the speedo stuck again my son hit the top of the dash really hard, the speedo worked again and the van popped out of limp mode and shifted like nothening was wrong at all. Only worked for a few miles and then popped back into limp mode again. I'm pulling my hair out.......lol. Any help would be greatly appreciated.

First thing I would do is get it to fail and watch for a Service Engine Light (SEL) on the dash. This indicates the Powertrain Control Module (PCM) has generated and stored an error code. This error code could give you a clue of what to look at. Disconnecting the battery resets the memory in the PCM and clears the code. You can cycle the key from off to on three times and count the SEL flashes to determine the code.

The speedo and limp mode problem combined does point to the in/out sensors but, if you can smack the dash and fix the speedo, the sensor is not the problem. There are many threads in the forum on this subject. Some talk about bad solder joints on the instrument cluster circuit board and/or connector. I recall something about melted connectors behind the ventilation control panel. Some talk about splices but, I don't recall any saying where they are. I'm fuzzy on older vans but, the TCM is a box about 3"x5" on the passenger side fender wall. Still trying to find a picture.

I second your thought on the tranny. It's not the problem.