I have already replaced the fuel filter and I use Chevron fuel injector cleaner every 2 oil changes. Any ideas? Vac. lines to check? Fuel Pump crapping out?
thats seems normal on your car . change fuel filter , if that doesnt help I would say its because of the headswap if you hadnt had the car tuned since you did that , if you dont have one I would put an adjustable regulator on and up the pressure some and see how it reacts . pump might be questionable but that pressure on your car is normal .
If that's your pressure across the rails that seems pretty normal. If there's no serious drop under WOT then you're at least getting fuel to the rails and holding pressure, so I wouldn't necessarily look at the fuel pump as the culprit. If the filter was gummed up that could also cause restriction in the lines, so your pressure at the rails would drop.
I would look at the tune and injectors. Do you have an aftermarket chip or reflash? You're probably putting out about 300 HP @ the flywheel which is taxing the 19# injectors a little bit, but they should hold up to that for a while (if not indefinitely). I'd get the a/f checked on a dyno and have the chip re-flashed based on the readings.