dash temperature gauge normal but I have a P0118 code obd@ shows -40C

Question

I have a 1997 GMC Safari 4.3L V6 with a W engine code. The engine starts when cold and runs well until it gets warm, then runs rough occasionally stalling and it is hard to start when warm. My dash temperature gauge seems to work normally . My blue driver obd2 is showing a P 0118 code and the live scan shows Engine Coolant Temperature is -40 C and stays there as the dash temperature gauge shows normal operating temp, and the heater is pumping out warm air.
Are there two coolant temperature sensors on this engine? I know of one located on the drivers side of the left cylinder head between the middle and rear exhausts. I have checked for another near the thermostat housing and can't find one there?
I am having a hard time understanding the discrepancy between the OBD2 reading which is consistent with the symptoms and the gauge which is consistent with the actual engine temperature.