Do me a favor. Get an oven therm or a probe thru a potato and place it in the center of the bottom rack. Compare the two and post the results. I have a feeling you are reading some heat leakage from around the bowl or you have a bad therm. Normally the bottom rack is cooler than the top. This varies a little as the smoker gets closer to finishing time. I would not bother to do it right now, lets not mess up a good butt!