1971 Chevy Chevelle No fuel to carburetor

Engine Performance problem
1971 Chevy Chevelle V8 Automatic

My car has not been getting fuel up to the carburetor (or the fuel pump). I thought I might have another bad fuel pump, so I replaced it. When I took it out for a test drive, it emptied the fuel bowl on the carb again & wouldn't fill it back up. So I dropped the tank & replaced the pickup sock. I also replaced the short rubber line that connects the tank pickup to the feed line for the fuel pump. I did blow out the line from the tank end to the fuel pump end (with the hoses disconnected) & the line is clear. I still could not get any fuel up to the pump. So I put my old pump back on, but double checked to make sure that the fuel pump push rod was moving. It has about 1/2 inch of movement when the engine is being cranked. I have dropped the tank in the past & never had a problem getting the pump to pull fuel. What could be causing this problem? Is there a priming procedure that I should try? Would it help to fill the primary bowl on the carb through the vent tube & start the car to get the pump operating faster? I really don't want to go to an electric pump. I also need to add that my motor has a Comp roller cam in it (non-billet). My builder told me it would be okay to use my Moroso light weight fuel pump push rod with the chromoly ends on it (he said it would not harm the camshaft or wear down the fuel pump lobe). I figure that since the rod was nice & shiny on the camshaft end with no signs of gouging or any negative stuff like that, that the fuel pump lobe on the cam is probably okay. I am tired of fighting this problem so any input will be greatly appreciated. Thanks in advance.