were the eccentric bolts for the upper control arms replaced ? if so, do the cams fit the brackets tight, or are they sloppy in the brackets ?
are the cam brackets straight, or are they bent or beat up some ?
i have seen replacement eccentric bolts that the cams were smaller than the originals, and while they would work to set the alignment, the alignment would not hold because the cams would eventually shift around because the diameter of the cam was smaller than the bracket.
i know it sounds impossible, but i chased that deal for quite a while. no matter how tight the nut was tightened, the alignment would last for a little while, then change for no apparent reason.
when the cam bolt finally broke trying to tighten it up super tight, a new cam bolt package was procured. when the package was opened, it was thought the bolts were for a different application because the cams were slightly larger than the cams on the bolt that broke. upon placing the replacement cam into the bracket, it fit very snug, with no slop, like the one that broke. put those bolts in, and no more problems with alignment changing.
this only happened one time, so i don't know if it was the wrong cam bolts for the application [i didn't put the originals/replacements in] or a bad replacement part.
since that time, when replacing cam bolts, i make sure the cams fit the brackets snug before installing the control arms.
just my experience. your mileage will vary.