No heat front or rear

I have no heat coming from the front or rear. I have flushed the entire cooling system, I have blown out both heater cores with water and air, both ways forward and reverse. I replaced the water pump, the thermostat. Previously I had replaced the front blend door for no heat in the front about 2 months ago and everything worked great until 2 weeks ago. I even packed cardboard in front of 3/4 of the radiator, now when I drive it tries to get lukewarm but at idle it goes cold immediately. The top radiator hose doesn't get hot which tells me the thermostat is stuck open. I just replaced bit 2 days ago. I thought about changing it out again, but I am getting frustrated. I have been a professional master technician for 40 years, I can't even read ECT with my Snap On Modis. All I can seem to find is cylinder head temperature and that value is measured in volts and it seems to be within specs.