Ditto to what he said...
With the 4" Susp. lift and 2" shackle lift, your rear driveline angle must be pretty severe.
Look into getting a sye and a cv driveshaft.
Check this SYE out, it's very reputable and the best of its kind:
NP231J HD Super Short SYE
With the SYE, you could either get a CV driveshaft (tom woods) or get the front driveshaft from a late model 90's Cherokee. They need to be cut and shortened, but will save you some money in the long run.
Either route, i would just get that fixed before it gets out of hand.