What thermo says it's 225-250? My guess is your temps at grate level or by the butt are well below that and probably 160-170ish. Chalk it up to experience and or order pizza, or most KFC's have 10$ buckets on Sunday.
Oct 2011 Update. (it changes)
2 WSM's 1 of each (18.5, 22.5)
2 UDS's Gone, (Brother in Law took them....FARKER)
1 Rib Machine Chargriller Pro Hella Mod (Retired)
2 Bubba Keg (One HOT MOTHER, One LOW N SLOW)
1 22" Performer
Yoder YS-640 is the next cooking device.