I think my U-joints are shot

[Jerry]

Hey cool stang, I got a 67 GT Fastback myself. Anyway, you can usually hear the u joints clunk when you accelerate or deaccelerate. You might try going under the car, grabbing the drive shaft and twisting it back and forth to check for abnormal movement in the joints.
Dont forget the obvious things like your tires being out of balance etc. Good Luck