Sounds to me like your smoker has a heat leak. When you hit 160, foil it, throw it in the oven at 275 degrees, and it will finish in no time. Even if your smoker says 220 - 250, and your meat is at 160, the smoker may have too much air flow. I have noticed on very windy days, i have to fight to keep my smoker at 200-225, and when my butts and briskets hit 160-165, they will sit there forever, so when it is windy like that, i just take em straight to the oven after i foil em around 160-165. Like i said, sounds like your smoker has a heat leak if there is such a thing, or too much heat transfer/air movement or something like that. Hope that helps.