I purchased a 1997 TJ Wrangler with a two inch lift and 32 inch BF Goodrich and for some reason the universal joint in my rear draft shaft always breaks within a two week period.
Check the yoke and make sure it is in good condition, and be sure the ujoint isn't pressed in too tightly. The ujoint should move smoothly with very little resistance.
Also, while your at it, check your lateral arm bushings. Sometimes when they wear out, it allows the pinion of the axle to tweak further than whats allowed under torque and cause a premature failure on the u-joints..