AC causes shifting problem

My 99 Caravan 3.0 runs fine except when the AC is on. It runs fine sitting at a redlight, but I have to turn it off while accelerating, otherwise it doesn't want to shift normally, it always wants to stay in a higher gear. Once I am up to the speed I want (35 or 65), I turn it on and everything is fine.

Any ideas?
Idles fine, runs fine, just doesn't want to accelerate like it should. This happened a month or so ago, it seemed to fix itself for a couple of days last week, and now back to the same crap.

That's an odd one. Since it's intermittent I'd suspect a poor connection somewhere, possibly at the Transmission Control Module (TCM) and eliminate a module programming issue. You might consider having a tranny shop connect a transmission specific scanner and check for tranny codes. Other than that I'm scratching my head especially with no other symptoms. Keep us posted.