Fuel pressure dropping while driving and under acceleration to zero at idle runs 4 lb electric Blue

What I was trying to explain in a earlier post I used an old highly regulator turn wide open as a t to supply both of my four-barrel carburetors. The fuel lab is designed for a return. I'm going to try to block the return line and run the supply line into a large container and see if I can get the 14 lb that the blue Holley fuel pump is capable of and see if it changes when I give it gas. I think that'll work as a test