sometimes when i shift into drive i hear and feel a thunk like theres a space in my rear end or something it does it sometimes if i am driving and i let off the gas and roll a little bit then hit the gas it does it too i baught new u joints but i havent installed them yet id rather do it all at once if its something i can do

 

Did you check the U joints first? The clunk isn't always the U-joints..

Grab the drive shaft and see if it has any play. If it does, that's your clunk. Otherwise, try and see if you can isolate it to an axle, and also check your motor mounts. A bad motor mount can cause the same thing.