1st things 1st, unless you have a wideband, I would not trust the analog guage(autometer ect) I know some people cant afford these devices, but a wideband should go hand in hand whenever you plan on upgrading/modifying your car, these days you can pick up a good WB for less then $300 and i some cases less than $200. With that said, I would run in the range of 28-36psi with the FPR vacume line on. If you are still running lean above the maximum pressure, I would look elsewere for problems. I run 780cc injectors and 20PSI and around 500HP(no dyno yet, just a guess) and I am running stock fuel pressure with line off. A bad O2 sensor will cause all kinds of problems, so I fit is old, and increasing your FP doesn't help, that and the fuel filter would be the first thing I would check, After that I would run some fuel injector cleaner in the car, If that still doesn't help, I would check the fuel pump, It might be going bad and having trouble keeping up(cant hold a steady pressure) 1 thing at a time, do the cheap easy things 1st then move on to the harder/more $$$ things, best of luck, and let us know what the outcome is..