I have a 2000 grand cherokee with a 4.7 v8 automatic Quadadrive. the front tires wont spin in fulltime, only in 4LO. any ideas in what is wrong with it?  

I used to be a Jeep Service advisor. Sounds to me like you have an internal failure with the Transfer Case. Doesn't sound like any differential or other issue. The Grand Cherokee models with that 4wd system around that vintage had quite a few similar problems with the transfer case. Either take it to a Jeep dealer or a garage really experienced with off-road equipment. I have seen lots of people get into worse problems with having a general repair facility fix things like differentials and transfer cases. Not a good idea.