My pork butts in the AQ typically take a little under 2 hours per pound at 225. If you cooked at 255, I suspect your butt was in the "stall" at 8 hours. Was the result at 8 hours tender (pullable, assuming you are shooting for 200 IT) and juicy, or still a little tough? If you'd let it go, I think it would have eventually resumed heating and got done in a couple more hours. I doubt the pan had anything to do with it.