Since doing the evaporator and heater core I've only driven the Jeep a handful of times to work, and only once since it has cooled off. So I thought I picked up on a heating abnormality, but kind of shrugged it off. Today it was obvious. Set the thermostat at 70F and left the house, as normal it took a few minutes to kick on and nice hot heat was blowing. Then just as I was getting comfortable, boom ice cold air. Turn the thermostat up a few degrees and it blows heat for a few, then boom ice cold air. Well I did a little research and it looks like I should check the interior thermistor, apparently if they are dirty this can happen. Also there is a manual step calibration for the blend door where it gets put in one place the ATC is programmed. Since I bought a used ATC it is possible that someone modified the program for some reason, or visa versa. So got to clean the thermistor then look at programming.