Having problems getting the griddle to go above 325. Cook says stuff takes much longer to grille on this thing ever since they got it used. Checked to make sure it wasn't an LP unit hooked to gas , it wasn't, orifice is a 49 on the one burner....assuming the rest are the same. Checked gas pressure with all burners on, right around 5 inches water column. The problem seems to be the thermostats shutting off around 325 on the surface. there are three of them and they all seem to be doing nearly the same thing. I adjusted the calibration screw in the center thermostat and basically no effect whatsoever. Looks like these stats are over 200 a piece. Is there anything else I can check?