All the above...agreed.
And, you can calibrate the factory GOSM thermo. I use a fresh calibrated (or checked) turkey fryer therm. Check the fryer therm buy partially submerging the probe in boiling water. Depending on altitude, but mostly the actual barometric pressure, the thermometer should read at or near 212*F (sea level). Higher altitude (lower barometer reading) will result in a slightly lower boiling point of water.
Use that freshly checked fryer therm as a probe for the cabinet, as close to the stock probe as possible, through a door crack, or hold the stock therm rotated 90 degrees off level and insert fryer therm into the line-up pin holes (clips must be removed). With the burner running, take up to a near smoke temp (200 or so) and cross-check the 2 readings. If stock is out of tolerance, let it cool and turn the hex (I don't remember the size, it's SAE, maybe 7/16") on the stem to correspond with the difference in the two readings, then, recheck to make sure you got it right. Advise not to adjust the calibration until temp is cool and stable, or your calibration will not be very accurate.
Mine was off about 60* when it was new. It happens alot, with all stock thermometers, so don't sweat it. Some can't be calibrated. These types with the hex "nut" on the stem of the probe can be adjusted.
Good luck, and may the thin blue be with you!