Bob, I think the altitude, and meat load, effected your times. First, the air at your altitude is less-dense than those of us down here at 1,200 feet. Therefore, it will take more heat to get the same ambient temperature effect of more dense air. If I lived in Colorado, I would up my temp by at least 10° on everything, and more in windy/cold conditions. Maybe some of the engineers will chime in, but my aviation background leads me to this theory.
Also, having that much meat in there effects time, and another 10° should compensate for that, too. All things considered, even smoking at 240° is pretty low-temp. No reason a couple of butts should take that long, no matter what the meat is like.