1995 Mustang GT Fuel Pressure reading at 20 PSI, Please help me.

I am trying to figure out why my fuel pressure is sitting at 20 PSI still, after I changed out my fuel pump, fuel filter, and fuel pressure regulator. It's not misfiring at all. I hooked a gauge up to the fuel rail, and before i changed out parts it read 20 PSI, same with after. Could my factory chip have been flashed at one time or what would cause that low of pressure? Is there anyway to reflash my computer? I had the mufflers cut out a while back to make it louder, would that have done anything? It runs like a champ, but just too low of a pressure reading. Any help is appreciated. Don't want to be buying parts I don't need to fix.