my f150’s heater wasnt working while on a trip to mexico. it wouldnt heat while driving sixty and over,and the tempeture gauge would drop to zero… I changed the thermostat and ther temprature sensor… And while the truck was standing still while running, the heater and motor temperature gauge would work fine.
I’m lost. What’s the question? Is it still getting too cold even with the new thermostat? Did you replace with the correct OEM temperature thermostat?