I hear the vibration only when I get off the throttle, or am on steady/no acceleration, normally around 2300 rpms or yeah right around 55-64mph.
Yeah I have been greasing the U-joints ever since lift and it does decrease the noise slightly, but it comes back in one day of driving.
Here is where I explained it when I 1st noticed it:
http://www.vehicross.info/forums/sho...t=13537&page=2