I have learned to live with the +/- 10 degree swings. As hotlick says, they aren't designed to run perfectly steady and honestly, the swings are a key contribution to the superior smoke flavor.
But your swings of 50 degrees are unacceptable IMO. A smart first step would definitely be to get back to factory settings which that chart you attached seems to be mostly that. Then try to dial it in from there. If no success, you definitely have a hardware issue.