Pinion threads are too small. It pulls the threads, junking the whole R&P. You can't ever reuse gears. If you're working with all brand new parts and solid pinion spacers, it'll last longer... but still won't last.
Sooner or later it'll get loose, or the pinion bearings will brinnell, or the yoke seal will start pissing fluid (they all leak, just a question of how much), and you'll decide that you need to tear it down to fix it. You'll pull the yoke off, take one look at the pinion, and realize that the only parts you can reuse are the locker and the housing. And you'll throw the whole damn thing out in the yard, go buy a 14 bolt, and build the axle you should have built in the first place.
Go through the junkyard some time and check all the 10.25s and 10.50s out there. See if you can find one that doesn't have endplay on the pinion yoke. Visteon knew it was a problem... why else do you think that they changed up the parts every couple of years? Long yokes, short yokes, different bearings, a whole new R&P set, etc.
