The slip yoke bushing feels fine, no leaks etc. There is about 1" of end play. I didn't say prior that I have added shims under the trans mount, moved the vibration up in speed and more significant. Also shimmed the diff down 4 degrees and made it worse as well. I'll try the jack it up and run it w/o the tires and see if I can see where it coming from. I did follow the truck down the freeway and could see the rear end bouncing when the vibration was present.