| Hopefull
The 92 to 95 s20 transaxle uses an electronic Vehicle Speed Sensor (VSS). I would start there at the VSS. This is located on the transaxle. Should be 3 wires coming off it. Yellow/White Yellow/Blue and Black. The Yellow/White turns into a Yellow/Blue behind the dash to speedo. The Yello/White turns into a Black/Yellow which taps into the PGM-FI Main relay (Fuel Injection Relay) and into an Upshift indicator light. Black is Ground. Just check to see if the connecting harness has any corrosion on the terminals. If not make sure the snap on connecter stays snapped into the connector. Then do a visual of the harness and wires to see if anything is burnt or frayed or do an ohm test if you really want (not neccesary). If everything checks out ok. I cant see it being behind the dash especially if you didnt take the dash apart. Then go to a junk yard and purchase one. Trial and error. Im not sure if you want to put an ohm meter on the VSS to test it cause the wheels have to be in motion to get a reading! I don't have the reading from a new one... If that still doesn't work its possible that when the tranny was rebuilt the circuitry for the VSS was somehow disturbed. | 
