Stalling/loss of power after getting after it.

I had a similar issue in the past using a Jeg's fuel regulator that looks just like yours. The gauge would read 6 psi but after driving the car around for awhile and getting it hot in traffic it would start to run rough, every time i would check the gauge and it would be at like 3 psi. I ultimately just removed the regulator entirely and it solved the issue.