Heater blowes cold air sometimes and sometimes it blows hot 05 Chevy hd 6.0

What is your question?

Replaced watterpump thermostat blend air door and hose to heater core is hot going in and coming out heater still blowes cold air then sometimes blowes hot 05 Chevy hd 1500. 6.0. Any ideals what is wrong no leaks or noises

What makes this problem better or worse?

Nothing

How long has your 2005 Chevrolet Silverado 1500 HD had this problem?

After I changed water pump