Skip under load
My 98 XLT Exploder (110,000 miles) just had a similar problem. I have the Auto 4x4 option and I noticed that under load, starting on a hill, in bottom gear loaded with a trailer, it would skip and judder. I finally tried turning on 4x4 manually in the same circumstances. It no longer skipped when in 4x4.
I concluded that it was the transfer case. My tranny shop confirmed it may be as they had seen many of them changed out ($1400 each!).
My delaership suggested changing the TC oil as a first step (hell; I'll do anything to save $1400). So far, 2 weeks into it, its worked. New oil in the transfer case has cured the problem.
How this relates to the a/c being on, I cannot say. Maybe coincidence or maybe my post is no use. Try turning on 4x4 when it does it, see what happens..........
Jethro


