so when accelerating starting at 35mph my rear end jumps and vibrates like crazy until at a steady pace and also if I decide to stomp down on pedal it won't do it any ideas

U-joint(s)?

Tires outta balance? Bent wheel?
If the whole rear end is shaking its not gonna be a u joint...if your getting a vibe look at your u joints

ujoints on driveshaft correct

it's who rear end

Yes... and along with the others a bent wheel. A tire bubble can do some of what you're talking about too, or tread starting to separate.

why would bent wheel stop when I get to steady speed or stop when I get on it won't it continuously bounce xj around if it was that ?? thanks though ahead time forcadvice

The wheel finds its balance point at said speed and trues up. could have spring issues worn bushing(s), just noticed it was a grand were talking about....OOPs

I guess besides brake stuff, the drive-line U-joints are next as far as what "goes" most often for me.

The frequency/vibration reminds me of a Trout on the line!

Jack one rear wheel. In park move it forward and back with your foot while you watch/feel the two U-joints. No play is OK. I only do the bad one, (probably rear), but others do both. The caps might go pretty easy if you heat the ears, but can be supper tight cold.

nooo it's a Cherokee I got a grand and a cherokee

Hence the post title..lol

why would you say grand then

Forgot the title and saw grand cherokee

it's cool so you think it might be u-joints

Yeah could be ... The slip yolk could be worn or a piece in the T-case? A broken tooth in the rearend? rearend wearing out and telling you about it? Does it clunk hard when putting it in gear?