NewB Q(Front DS,U-Joints,Clunk Sound)

Alrighhhty I have an 89 xj 4dr auto w/ np231 w/ 3" lift and running 32's and whenever I'm in four wheel drive I hear a clunk sound up front and I think its my driveshaft or U-joints. I have 330,000 miles on it and they've never been replaced. When I go 4 wheelin' for a long period of time the clunking or pop sound starts to get worse and clunks/pops more often. I think it also might happen more often when i'm over the 20 mph in 4 high, but not completely sure. And for the U-Joints, when I upgrade what should I upgrade to and where can I buy them??? and also do you think I would need to replace the front driveshaft also because its never been replaced... I'm in need of some help and opinions. thanks rob