You should check that your voltage to the pump is constant across the rpm range. If you are running vacumn to the fuel pressure regulator, the opposite should happen as mentioned. There is a relationship between volume and psi as well. If all things are as they should be, then you are no longer running the engine off the pressure regulator, but the injectors at high rpm. Rather than the regulator bleeding fuel back to the return, the injectors are bleeding the fuel pressure into the engine. You may need to increase the volume your pump is putting out. We use the Bosch CIS pumps on all our cars. These are high volume rotary pumps suited to a regulated 80 psi. They are cheaper than aftermarket performance pumps, readily available, and reliable. A good quality regulator is also a must. We use ones made by aero. Not sure how much of this is IT legal though.