Thanks John,

I'm pretty sure it's not the clutch. I replaced it a year ago. When I'm in 3rd gear driving 30 mph, the engine feels like it did when running at 40 mph before the valve adjustment. I was driving down a hill today at 60 mph and the engine was reving too high, so I coasted in neutral for a short distance, then popped it back into 4th. The engine raced, and the car slowed down as if I had put it into 3rd gear. I'll try again tomorrow, and hope I have'nt ruined anything.