Driveshafts

[BLKF250]

yeah i had to remove both of my drive shafts( i have 4x4) cuz i had to drop the trans i marked them before i took them off but now i got a little bit of viberation iam probably the only one to feel it cuz i drive the truck everyday. Iam assuming the weight needs to be adjusted on them. but my question is which driveshaft is it? my guess is the back one cuz the front one doesnt move until i put the truck in fourwheel drive. How can i tell its not balance right? Where can i take it to get it balanced?...Not all the time but sometimes ill go around turns and here a big clunk noise that i believe is coming from the driveshaft and i want to say thats happening cuz the shaft isnt balance right