Missing under load

Yes but, the fuel pressure should vary with manifold vacuum. It should be less at idle, and increase at WOT, if that is not happening something is wrong. A pinched return hose is an example. A 1 psi change that you suggested raised a red flag.
His fuel rail does not have a vacuum actuated regulator. There is no return line on the later models.The pressure regulator is located in the fuel module inside the fuel tank.