OK, I have the exact OPPOSITE problem -- one we've never had before.
Started an 8 or 8 1/2 lb butt yesterday around noon. Ran it at 215 in the Egg all day yesterday, lowered the pit temp to 195 for the night. Pit temp was steady at 195 at 0500, butt temp 160 degrees. Bumped the pit temp to 200. 5 hours later, the butt was still 160 degrees. (This would be after 22-ish hours). Bumped the Egg temp up and up and up, to 225, then 250, then 275, and the butt temp only got up to 168-169 over the next 5 hours. Bumped the temp to 325 about 3:30 pm, but the meat temp was still only at 170 degrees at 5 pm. Finally cranked the pit temp to 375, and the meat temp got to 180.
The thing's GOTTA be done, so we're going to pull it out, wrap in foil and put in a cooler for a half hour or so.
My question is... has anyone else ever had a butt that plateaued out on temp and never did get past the plateau? I've always got to a point where it held temp and then increased to 180 or so, then increased the temp to about 300 until the butt got to 200 degrees. But I've never had a butt this size take over hours to cook!