First, Jeff, I recommend you stop wasting time monitoring box temp. Is the food coming out good? If so, then it's averaging to your set temp. Secondly, you're going to drive yourself crazy chasing temp swings on a smoker that big, with nothing but a loin or some chicken breasts in it. That's not much of a step from an empty box (volume-wise). When you load it up with a Boston butt or two, or a big brisket, you'll see much smaller swings. But, back to the first recommendation; trust your smoker, if the food is good!