Mechanic said pressure was on low side at 45 P.S.I. which it still is now after replacing fuel pump. I installed an aftermarket fuel pressure regulator and the fuel pressure dropped 5 P.S.I. and the performance dropped with it. I put the original one back in and performance went back up. I actually suspect a faulty injector but need to rule out the fuel pressure regulator first. I actually found moisture in one injector connector. After I cleaned and dried it my light throttle stumble went away but I can still hear a light misfire sound in the exhaust at light steady throttle and overall performance is down. I thought maybe if the aftermarket fuel pressure regulator reduced performance by dropping fuel pressure 5 P.S.I. then maybe raising it 5 P.S.I. would put me back on track. So I need to verify or rule out this theory by properly testing fuel pressure. I hope this clears things up a little. Thanks