Problems

Fluctuation to a high point then down to a low point is normal for an analog based system.  For it to be more precise, you would need a digital controller that would cut off power to the element within a degree or two of the set point and turn it back on when the temp dropped a degree or two below the set point.  And you would pay good money for a truly reliable digital control.  I would not worry about it.  Auberins makes such a control that regulates the temperature digitally if you are interested. But it is not inexpensive.  And I do not know how reliable it is.  For what it is worth, I would not worry about the fluctuation.
 
The dirty little "secret" is that this is common, as Old Sarge says.  Your oven is the same way.  There can be a range of overshoot and undershoot of maybe 50-75 degrees!  For the most part, this isn't a big issue with meat.  It will average out in the end.  I can say the Smokin-It smokers are very well insulated!  They will keep a lot heat inside once you turn them off.
 
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