Emerson VCR755 Tape Speed Fault

I got the transport sorted out; all modes work fine now. In play/record, the tape speed starts out quite high, and slowly ramps down over 2-3 minutes but remains at about que/review speed. The auto tape speed indicator doesn't change with tapes recorded in SP,EP modes. I think it was doing this just before the transport got out of time; not sure. I swabbed the side mounted tape heads, but haven't cleaned the drum. How is tape speed sensed, and could it just be an adjustment? Que/review in play work ok, just quite higher than normal. Ideas? JR