What goes out is the rear CV on the front shaft. When the differential is dropped down further away from the frame, the angle of the rear joint is put in an almost bind. I only got 4,000 miles(if that) out of my stock shaft(the kit went on at 70,000). Yet others report 30,000. When the joint goes, it'll make the truck shake and make the front end feel like it's falling apart. The fix is either getting the $450-550 Superlift shaft or making your own using a 95-97 Explorer front shaft, shorten it, and use an adaptor to join the 98+ CV Tcase bucket to the explorer double cardon shaft. I built mine using all new components for under $300...can be done using a junkyard shaft for under $200. You'll end up with a shaft exactly like the Superlift shaft for about half the price.
IMO, the Superlift is a very good kit....the best one of the 3 that were made for 98+ Rangers. Trailmaster had a 4" that was very similar to the Superlift but used balljoint spacers, which in my opinion is kinda sketchy. The 5" RCD needed work ontop of the $2500-3000 price tag....saggy coils, diff drop bracket that snaps in half, and the fact that it's only designed for 98-02 trucks....anyone 03+ would have to downgrade their front brakes to smaller rotors. Only problem with the Superlift is the crappy sway bar end links.
Only kit in production for 98+ 4x4 Rangers that's just a plain lift kit is the 4" Superlift for the price of $1500. The other option is the long travel Dixon Brothers kit which gets you approx 3-4" of lift and tons of wheel travel for the price of upwards of $8,000. Camburg may offer a 98+ 4x4 kit, but I am unsure of that.