Caster and strut rods
I had the same thing happen--the alignment guy could only get to about 4.5 deg. positive before the threads ran out. The problem is that the frontside bushing at the LCA is too thick. This keeps the flange on the strut rod about 3/4" too far away from the front face of the LCA, making the rod sit 3/4" too far forward.
At the frame end, this puts too many threads in front of the frontmost nut, where they're useless, while leaving too few threads on the rear side to set enough positive caster.
Using too thick a bushing also leaves too little of the strut rod at the back end to get that big closed nut on all the way (which may let it contact the spindle.) It's threaded an inch and a half deep, and the Moog bushings I'm using only let me use about half those threads. I don't like that, because that nut takes a lot of force in turns.
I heard that Ford used two lengths of bushing for the LCA end of the strut rod. If so, TRW, Moog, and the other aftermarket companies may have reproduced only the longer one. The dealer quoted me (no kidding) about $75 per side, but I don't see any other solution.