1995 ford Explorer speedometer,trans issues

I have a 1995 Explorer had two trans rebuilds in the last 6 months recently I had a rear end put in used to save money then they repaired the trans and put heavy duty cooler in truck. Few days later and 500 miles speedomter started to jump around from 65-0 all over the place and at lower speeds trans doesnt shift right. I was told that the trans shifts with the speedometer so if the so if speedometer isnt correct then it wont shift right. I took truck back to shop and they said they tired to replace the speed sensor but it didnt make a change so it was a wiring issue. I have been told so many stories can someone help me with this please

The PCM controls most of the transmission. Either you do have a wiring problem, or the PCM may be bad.