About temp swings,with only a single potato,over an hr,or so 40º-50º wouldn't be considered wild swings.
You can bring your own remote,wired probe that you know is correct and put it thru the potato.The potato is just to keep the probe from resting on a metal rack.
The other approach could be set it at the max and see high it gets.A full load can greatly reduce swings in temp.Leave the door closed,as that causes your swings,as well.