You have what is known as the returnless fuel system. That means that there is no return line and no fuel pressure regulator in the return line. In the returnless system, the fuel pressure is controlled by the PCM (computer). There is also a module that takes the readings from the PCM and doubles it before sending the signal to the fuel pump. It sounds like it may be that module that is acting up. I don't remember where it is mounted. Maybe someone else does.
