4th gear 2800--3K rpms

Go put 30 or 40 miles on it and them come back, jack it up and put your finger on all the u joint. They should be cold to the touch. If you find a warm or burn you finger on one.........Well you have found your problem.

Also if you slide the yok off and didn't put it exactly back the way it came off, they well be out of faze and cause a lot of vibration.