Search First, Ask Later young one. A search will of yielded many answers to your questions, and they would of sounded like this.
A 5.5" superlift is the highest lift possible for the 1st gen TTB, you can go higher but thats with a body lift, which has no effect on driveshaft length. A 5.5" superlift requires no driveshaft work and shouldnt effect reliability, just drivability. Mine has a 5.5" superlift and 3" bl and its reliable as anything else out there, buts it no where near as driveable. The also make 4" and 2.5 and 1.5" lifts for your X, all without modifying your driveshafts. Some claim to have problems when they lifted their X with the 5.5 kit with the driveshaft being overextended but from what Ive seen and heard it isnt a very common problem.