So facts- 99 xj stickshift, 3" zones lift (leafs and coils), recently new clutch (6 months ago), new cylinder head, 31x10.50 tires, new rear driveshaft u joint. I know my passenger front u joint is bad. Vibrations didn't happen before the lift.

My issue;
Vibrations under acceleration only. On the dot, no matter the gear, I get vibrations at 55 mph to 60 mph and then they cease. I can kind of replicate the vibes with strong throttle on very low rpm. Some say it isn't bad but near the passenger seat(from what I can tell) you can hear things begin to rattle.

So my next step is to replace the front u joints. Than off to the shop. I really do not want a slip yoke eliminator. I could move the yoke on the output shaft up and down but not side to side. I think it is an output shaft bearing but I wanted to come here and see what others suggest.

 

Drop the transfer case down.