Lynn Blackwell - Just curious, which park are you in north of Houston?
Can you try switching the thermostat from the working unit to one that's having issues, that would at least tell you if it's a thermostat issue. Our unit had a defective thermostat from the factory, it was off by 8 degrees.
2015 Pinnacle 36FBTS
2015 F250 SD Platinum 4x4 - 6.7L PSD :
Titan 50 Gal. Fuel Tank
Slotted and Dimpled Brake Rotors
Air Lift LoadLifter 5000 Ultimate Airbags with WirelessAIR Controller