Oven temperature all over the place

I slide the oven out from the counter and unpluged it. I removed all the oven racks. I then removed the machine screws that held the sheet metal that covered the back of the unit. This made it a lot easier to disconnect the long oven sensor wire and put the wire through the insulation. I removed the two screws on the inside of the oven that held the sensor onto the inside rear wall of the oven. The old sensor did not test too bad but the temperature is reaching the set temperature. I still had to adjust the oven temp up ten degrees using the control panel. I have learned that it takes a few cycles of the element going off and on during the warming to reach the desired set temperature. One more issue is that the buzzer goes off signaling that the set temperature has been reached when it has not. When I set it for 350 F the buzzerr goes off at 280 F and I have a good oven thermometer. I own three oven thermometers and they all read the same. We use to have nothing but Maytag appliances but no more. We have had issues with Maytag front loading washers and ranges. PartSelect is great. Good prices and fast delivery.