92 trooper ECU issues please help

I have an intermittant problems with my 92 Trooper. Occassionally, the speedometer will stop working. It might resume working or it might not. Usually the next time i start up, it's working again. if the speedo quits and doesn't come back, after a while the "check engine' light comes on, and the engine will stall out at traffic lights unless i ride the gas pedal.
had it diagnosed and the Vehicle speed sensor tested bad. so both the front and rear speed sensors were replaced. (at different times by different techs)
the front one was off a wreck (allhyundiaisuzuparts), the rear one was new (ouch!).
no noticable changes in the symptoms.
the next issue is after driving at about 70 for a hour, the car began lurching and slipping. letting it cool of it seemed OK again. tranny shop found nothing wrong, but I noticed the fluid was high on the stick when i checked it. if the shop overfilled my tranny, will this maybe cause the fluid to foam up and then slip? There does not seem to be a way to drain the tranny without dropping the pan. is this true?

finally my O2 light came on and won't go out. this seems to be unrelated to the other issues and doesn't seem to matter, my gas mileage is consistant.
For the speedo issue, whihis the one that is urgwent: maybe i got a loose wire on the ecu? how do i get at it to inspect it?
i got a auto 4WD 4 door. we like it and need to keep it going.
HELP!!