INTENSE VIBRATION 727 Duster!

well heres what happened to me, I installed new u-joints on my ds, with my new motor and I forgot to install the "C" clips on the new u-joints so that my driveshaft was not centered on the rear yoke, and I had the same vibration anytime I went over 45 mph, but that might be too easy, should still check it though, sometimes the easist things are overlooked.