You should definitely replace the fuel pump, the filter, and probable the regulator too. There is a check valve built into the pump and another one in the regulator, that is supposed to hold the pressure for you. It obviously isn't doing so. The pressure should be holding over 20 PSI for at least 1/2 hour. That and the return line is definitely part of the prob. Your fuel system is basically marginal --- it has the pressure but can it keep up when you are on the gas, is the question. So check into all the stuff I mentuioned. Its cheap insurance for a new engine.
***--- Wrecking Crew member ---***
"I've prolly been around longer than you think"
91 YJ 2.5L 5-spd, 31" BFG ATs, mostly stock NO RUST 160K in WNY, Daily Driver