Front vibration or do you feel it in the seat of your pants? If front then wheel bearings would be my first stop. if its in the back, I had some new U-joints that weren't properly greases and that caused some vibration in the rear at speed. Also these 2nd gens are notorious for Pinion angle problems. I had to add shim to the rear end and use spacers to lift trans that helped a lot but I still have a slight high speed vibration I cant figure out.