1993 Geo Prizm Instrument cluster or VSS problem?

Electrical problem
1993 Geo Prizm 4 cyl Front Wheel Drive Automatic 98K miles

So I bought this geo prizm with the speedmeter not working. The only time it would move is when I went on the freeway and it would shoot up to 70 then go back down to 0 once you slowed. Decided to try and fix it myself by cleaning the solder joints on the back of the speedometer by taking the instrument cluster apart. When I put it back together the speedomter started working but the O/D light started blinking after a few minutes on the road and the transmission isnt shifting right. The check engine light went on but when I turned the car off it went away and doesnt come back on. Took it to a transmission place and had the diagnostics read and it siad "vehicle speed sensor" and this list of solenoid things that werent working properly. My question is should I replace the instrument cluster or the VSS? I heard it could be the instrument cluster instead of the VSS.