Not developing pressure in cooling system

I can drive this thing all day and it never develops any pressure.
I figured the head gasket was bad(It was) and I replaced it and put a new head on as well.
No leaks, oil and coolant are not in each other.
I had to drive it onto a hill to 'burp the system, as it had a bubble in heater core.
Heat is now working, but still no pressure.
Pump is moving fluid, new thermostat. No leaks.