Bad Vibrations

[highlanderpride6]

I have a 5 spd 98 Tacoma with a 3 inch lift and running 32's. Lately I have been hearing a vibrating sound coming from around the back of the cab. I usually only hear this sound when I press the throttle. I have changed the bearings in the rear end and the U-joint on the rear drive shaft to no avail. The front two joints seem to have no slack in them. Do you have any suggestions as to what the problem might be.

[Hoodlum]

When you did your U-joints did you make sure to match up the factory balance line. It's a yellow mark on both the shaft and the slip yolk. If not your driveshaft is out of balance. I would start there I did this awhile back and mine was a spline off mark. Got my marks lined up and no more vibration. This is atleast a place to start. It could be something else.