I've had my 590 for 3 years. It has never been good with keeping correct temps and after a year of overcooking on long cooks I now always use two thermeters to keep correct temp. Usually if I set the rectec at 230 it will cook at 255-260. Today it was raining and I had to turn it down all the way to 200 in order to cook at 275-300. Anyway to fix this?