Heating problem on 2001 Ford Expedition

No heat front or rear. Have hot hoses at the firewall. Replaced thermostat (twice), burped the system, replaced radiator, replaced water pump, flushed system. Blend door appears to be working by switching from cold to hot you get some variance. What would make both not work?

Asked by for the 2001 Ford Expedition
Engine termperature or an air pocket still. You are correct to be looking at the engine, since temperature control would be odd to have a problem in front and rear both.

With all those components and the existance of the auxiallary rear system, I would really spend extra time to work on getting air out. Hopefully that's all that's left.