This is just a guess given the info you posted.
1) I would say you have air coming in from somewhere besides your Stoker causing the erratic temperatures you were having.
2) It would seem that your pit probe or your meat probe isn't correct. But you didn't say what you were cooking or how big it was.
Have you checked your probes in boiling water to check them? Did you use a different thermometer in the meat to make sure what temp it really was? Your meat probe might have been in a fat vein causing a incorrect reading.