Not sure what is going on. Are you saying that the smoker gets to your set temp via the auber then drops 15 degrees before cycling back on? I would start by checking the box probe and make sure it is clean. Also, do you have the analog controller cranked all the way on high? If you are getting to temp,is it taking longer than normal or roughly the same? Check your element in the dark when fully heated. Is it uniform of are there dull or extremely bright areas?
Here is a link on testing and what to look for:
http://www.appliance411.com/faq/test-element.shtml
And a short video on ohms testing the element:
https://www.youtube.com/watch?v=X8w1w45TrnU
Hope some of this helps.