Bad shaking in rear

so i went wheeling this weekend on saturday and the drive to the area was fine but on the drive home my cherokee started shaking in the rear really bad but only above about 45mph and only when im giving it gas. if i let off the gas the shaking goes away instantly. when im at a stop and just start going i can hear a pretty loud vibration in the back but i cant really feel anything until i get about about 45mph. again it only happens when i give it some gas. just wondering if anybody on here can help me out on what they think it could be.

ive got a 93 cherokee 2 door with 6.5 inch lift and 35" tires with 4:11 gears. dana 35 rear and 30 front open/open. i was thinking it might be either the ujoints on the drive shaft or maybe something to do with the shackles? i dont think its the weights on the wheels because it only happens when im putting power to the wheels. or maybe im wrong? lol

check u joints. they do the wierdest stuff. make sure you also just crawl under it and check everything for looseness, damage, etc.

Check to make sure your lugs are tightened.

x2 on the ujoints. Do you have an SYE? If not, that'll really wear out your rear ujoints.

ok thanks. ill check those 2 things. yeah ive got a sye