have an 00 ek swaped to gsr...speedo was working fine...after swap to ls...speedo stopped working then periodically would come back on...when it comes on it will work fine up untill i get into high rev then it will malfunction and spike by about 20 miles per hour, when the rpms drop it will go back to the actual mph...and then sometimes go back off... tried changing ecu...didnt change....changed alternator < read about something similar, didnt work

 

clean the connector that plugs into the VSS in the trans.

 

kuh ill try that today.