42 = ESTThe truck is now throwing code 42 along with the code 13.
The service manual will have a complete diagnostic chart for that code.
Verify engine temp, perhaps with an infra-red thermometer on the thermostat housing or upper rad hose. If it really is that cold...pop in a new thermostat, see what happens.I have been noticing that the temp gauge is on the colder side, probably sitting around 150°F-ish, and it fluctuates from 150ish to ALMOST 195.
Make sure the fan clutch disengages when cool--not seized and "always engaged".