Re: 6.4 belt change
50K is about right before the belt ribs have worn enough on a misaligned drive. If the squeak or chirp stops after running some soap on the belt ribs, you've isolated that misalignment is your issue. Its in the belt path and unless the misalignment is obvious, they are not easy to troubleshoot and its often easier to just change the belt when it gets pissed. Tolerance stack affects all of the brackets, pulley/accessory location, etc.
Swap the belt and it should stop but will come back within 50K miles. Belts last far longer than that (we have heavy truck accy drives that last 250K), but unless the alignment issues can be found, it is what it is.
Our guys in our replacement group at Gates are always putting new stuff on the web so perhaps there's something there.
2000 F250 CCSB-- GT4294R, 250/100s, Dahl/Fuelab, PHP, scan gauge, stock 17* pump
1994 F250 4x4 SC (sold)
1997 F250 CCSB 2wd (sold)