Odd vibration

I put in new U-joints. Now while driving at certain RPMS (load at 1K, 1.5K and a bit over 2.5K) the truck ahs a odd vibration. It started to vibrate when the Ujoints started to go, then it got worse and worse. I replaced the U joints and it got a lot better but its still there. What else should I look for? Wheels seem fine, no mud packed or anything.

1990 MJ with 2" of lift (lift is old)

many,many,many,many possibilities. Any bushings, tie rod end joints, tires out of round, alignment, ball joints.... Search for "death wobble" to see likely culprits for any vibration.

if you have a SYE then you have a slip yoke in your drive shaft, it does have to be in time

Transmission mount????