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It seems to me that you can see water churning in the expansion tank with the thermostat open and the engine revved to 2500 rpm. If you want an even more obvious check, remove the thermostat completely. You should have flow at all times.
It sounds like you either have a large amount of air in the system or a defective water pump. The other less likely candidate is a slipped damper making the timing mark inaccurate.
By the way, what's your idle vacuum running?
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