I have a propane master forge 2 door. Started my brisket and kept at 250 since 6am. I'm less than 4 hours in and the MES-73 thermometer is reading 172. Is the probe in wrong? Is it possible it's already that hot? It's a 6.5 lb brisket. I was going to foil at 170 degrees but I'm skeptical if the temp is right? Need some advice - quick!