If you set it at 450 what happens? The control does not accept 450 or the oven does not fire up anymore to get to 450?
I'd first ohm test your oven sensor. I use this multimeter myself: Multimeter DM10T
To ohm test the oven sensor: All you do is pull your range out from the wall, then unplug it, then remove the back access panel and you will see a little plastic connector that connects to your oven sensor, just unsnap that little plastic connector and take a ohm reading on it at room temperature per the video below.