A while back I posted that my 62,3/4, long bed, Chevy step side had a bad rebuilt "engine" vibration that started around 30 and got progressivly worse. Driving 65 was not pleasant. I had my mechanic replace the clutch/p-plate and that helped a little but only with the "engine" vibration. I told him that I wanted the drive-shaft balanced. To this he replied, "I think that we're [censored] in the wind". He finally agreed and we had it balanced. Problem solved!
btw: You can see my truck in the Gallery but the email link is wrong.
