DIAGNOSIS The oven's calibration is out of whack, or the temperature sensor (the same one that can throw an F3E0 error) is giving bad readings.
FIX You can calibrate it. With the oven off, press and hold the "Bake" button on the control panel for about 6-8 seconds until "CAL" or a number appears. Use the temp up/down buttons to adjust the offset (e.g., +35 if it's running 35 degrees cold, -20 if it's running hot). Press "Start" or "Enter" to save.
IF THAT DIDN'T WORK If calibration doesn't hold or you can't get it close, the oven temperature sensor is likely faulty and needs replacement (part # DG94-00607A). Its resistance drifts over time.
HEADS UP Use a good standalone oven thermometer placed in the center of the middle rack for testing. Door thermometers or quick-read probes aren't reliable for this. Also, all ovens cycle, so take an average temperature over 20 minutes.