From anything I've ever heard, the way to go is to get a CV driveshaft from someone like tomwoods, and get a SYE, which stands for Slip Yoke Eliminator. From what I understand, this is actually an extremely common problem when lifted 3.5''+. An SYE makes it so, essentially, the yoke can't slip out, and gives you a few more inches to work with. I don't understand the technicalities; I've never had to deal with it. I'm on 31X10.50's with no lift and TJ flares. Someone else here though (plenty of them around) knows alot more than I do. I've seen many threads about this, and JP magazine talks about it a fair amount as well.