Your not going to get a consistent temp with your pellet grill. The Non-PID controller is design to swing the temp based on how the system feeds pellets. Now with a PID controller will give you a more consistent temperature unfortunately the Austin XL has a non-PID controller.
Yep, what Dave said the temp swings are normal and nothing to worry about unless you have it set on 250 or something and it jumps to 400 or something during a cook (sometimes temps will rise when you first turn it on).
The "P" setting means "pause" and only works in the smoke setting.