Fuel pump problems

[BLP]

I am having some fuel pump issues. I have a blueprint 496 crate motor in my 1971 suburban C20. I have been having this issue with the fuel pump not pumping when the engine gets up to temp. about 190’. It is all good when it is cool, good flow and 8psi. But when it reaches 190 the pressure tapers off and I can see the fuel filter start running dry. I had a Holley mechanical fuel pump that I now replaced with a new edelbrock pump. I removed the gas tank and made sure everything looked good inside there. I also removed all the fuel lines and blew them out with compressed air. I replaced all the rubber hoses with new. I thought that maybe what I was seeing was water in the fuel filter so I put 2 bottles of heat in the tank after inspecting it again. I have now replaced the fuel pump push rod with a new high quality one and still after each thing I did it does the same thing. My current thought is when the block is warm that passage for the push rod tightens down not allowing the rod to pump the pump. I have run a hose from my fuel pump to a jar of gas and it did the same thing. The engine only has a few 1000 miles on it. I don’t really want to go to an electric pump but that seems my best option. Does anyone have any ideas on anything I can try? Thanks for any input. Sorry for being so long.