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50 psi is not enough it needs 52 - 59 psi, you might have a bad fuel pressure regulator or not enough voltage at the fuel pump.
If you believe the fuel pressure is now good another expert here suggested this to me
"If you have the ability to clear the codes, unplug the EGR valve and run the car with it disconnected. It's worth a shot. We have been finding some of these 3.1's with bad EGR wiring. The last 2 had a broken wire at the plug and caused this same problem. We thought it was the valve at first but turned out to be wiring."