Is it just at 60 mph that you notice this or is it the the same rpm range that you feel the vibration? It could be anything from the harmonic balancer on the front of the engine to the balancers in the engine to something happening to the clutch or input shaft bearing. Usually at 60 my car is pretty smooth, but I do feel the trans making a little vibration. As I rev the engine up the engine makes more vibration. Toyota put balancers in the engine to help stop that, but they had to lower the red line because of all that rotating mass. The 92 engine has those balancers.
Let us know if we are getting close!
Russ
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