Without getting into too much on the details on Teraflex, their main fault is that they keep the stock upper CA's which causes bad geometry with the pinion angle.
The rubber boot on the driveshaft coming out of the TC is actually on the transfer case, not the drive shaft. It just protects the splines of the transfercase output shaft and has grease under it. You can pull it back and look at it.
A TC drop isn't really necessary even at 6" if you get your pinion angles set up properly. I am at 6" and have on super minor vibration that I just havent' bothered to eliminate...
FWIW (For What Its Worth) Claytons is the bomb! It is more expensive, and requires more modifications, but it can't be beat offroad IMHO.
'04 WJ, 6" Clayton LA's, 242 SYE, 35" BFG MT KM2's, 4.56 gears, & D44a locked
'14 WK2 Limited - delivery pending:)