94 astro over heating problems

We have a 94 astro van, 4.3L Z series, it keeps overheating once the temps get above 40. He has replaced the thermostat, the water pump, hoses and we bought a new radiator. The radiator is still not circulating. He's tried "burping" it but it still doesn't seem to want to circulate. Now, he's finally getting some pressure from the radiator after he replaced but still no circulating and it's still over heating.

Anyone else have any other suggestions?

Was the water pump a remanufactured unit? There are two different impellers used on SBC water pumps. One is used for "normal" rotation operation, or the type that was used with the old standard 'V' belt drive systems, and a "reverse" rotation unit used with the later design poly-V ("serpentine") belt drive systems. Since the poly-V belt wraps the pump sheave on the top side of the belt in most later applications, the rotation direction is different. While a centrifugal pump will move some liquid regardless of which direction it rotates, it moves a lot more liquid while rotating in the correct direction. I've encountered this a couple times before with remanufactured pumps. Unfortunately, the only way to verify is to remove the pump and rear cover to inspect the impeller.