Whirlpool built in oven not holding temperature

[HomeStar]

Hello,
The model # is RMC305PVB00
It is a built in electric oven/microwave oven.
The electric oven will not hold temperature. Example: If you set the oven to 350 degrees, the oven counts down about 6 minutes and beeps alerting you that it has reached 350 degrees. But the temperature is not 350 degrees. It is 325. If you want 20 minutes the temperture is 375. After 40 minutes the temperature is 400.

I suspect the thermostat is out. I've ordered a replacement. It it round with two tabs for mounting and two tabs for an electrical connection.

I have two questions. Am I on the right track by suspecting the thermostat? Where is the thermostat located (does the range have to be removed)?

Thanks!

[JWWebster]

These new fangled ovens use a sensor. The oven sensor sends messages to the oven control. Without it the control don't know squat. AND the sensor could be what is killing the oven control. I would go with an oven sensor first and if that didn't work I would go with a control. But that is just me.