These things are HORRIBLE for air locks. Any little air lock will trap in the heater hoses and cause no heat at an idle. Since they appear to be the highest spot in the cooling system.
When looking from the front of the car, you'll see the two heater hoses loop up behind the throttle body area. When the engine is cold and there'* no pressure in the cooling system, remove the one on the right where it hooks into the metal pipe. Get a small funnel to fit into the rubber end and fill the hose (which fills the heater core) with coolant until it'* full. Then fill the steel pipe the same way and quickly put the rubber hose back onto the steel one with losing as little coolant as possible. Run the car at around 2500RPM until the thermostat opens then let it come to an idle, should be a lot better if not perfect. Might have to repeat again to get it 100%.
2000 Silverado RCSB 5.7L LS6 - 5 speed (Ex 4.3L V6)
T4 Turbo/Intercooler, Lunati cam - 220/224 .575/.575 112lsa, 317 heads, Edelbrock shorty headers, Magnaflow cat-back, CAI, Nelson Performance tune.