mkpedboy- I've never used the XP version of the PC, but I *have* corrected my YukonXLD using the M105/M205 twins.
Even with the XP model I wouldn't be surprised if you need to use 4" pads for timely correction. The only way my (older model) PCs will do it is with the little pads and yeah, I tried the KBM method with the larger pads before giving up and switching to my Flex (and/or 4" pads on the PC).
Yeah, I've discussed my experiences with
Kevin Brown. For serious correction on hard clear (like on Yukons) the SurBuff pads sound like a good idea; he *really* likes them for aggressive work like this. The fact that the marring didn't come out simply shows that a more aggressive approach is called for.
Correct, the M105/M205 twins don't break down, they dry out in the sense that the carrier agents/oils evaporate. Revitalizing them with waster/#34 can work but can also be risky in the sense of causing not-so-micro-marring, espeically if you make a mistake and get product clumping on your pads. I wouldn't recommend it unless you know what you're doing (in which case you won't be asking

"don't try this at home, kids" applies here but it does work well for me).
Don't spread M105. Put the pad on the panel and start working.
Work small areas, maybe 1" x 1" at least until you have things sorted out. Stay with that one area as long as it takes and see *what* it takes to correct it. No point doing the whole thing until you know what to do.
Expect to go over moderate marring quite a few times; the GMC clear is *hard* and M105 isn't all *that* aggressive on it. E.g., I did some areas eight/more times when doing spot correction with 4" orange pads (and PFW wasn't much faster). You won't correct it in one/four goes with M105 and a random orbital unless the marring is *VERY* shallow.
Pick one panel and work *that* until it's OK. Maybe do one panel after each of the next few washes. Heh heh...the roof can take a while! I did the whole truck all at once but it was one *VERY* long job over a few days.
Depending on how bad the micromarring from the M105 is, you might need to use M205/orange for the first follow-up.
The clear on my GMC was hard enough that M205 finished quite nicely with polishing pads, but I did do a final buff with finishing pads (but that was on the Flex). Even orange pads/M205 will leave the finish marring-free to the naked eye, the softer pads just bring up the gloss (probably more than you'd expect).
The polishing oils from M205 can result in pseudo-holograms that resist IPA wipedowns. Don't give up, they do wash off eventually.