fuel pressure regulator

99 GC. Vehicle was running poorly, changed filter-regulator. Helped for 1 week.
Checked fuel pressure, running at 20psi, changed pump. Still running poorly, pressure at 22psi. Pressure immediately goes to 0 after pump cuts off. I can blow through filter-regulator lightly and cap outlet side and get air through the return. I don't think air from lightly blowing should be able to get to the return port.
Any thoughts??