I have a 90 chevy truck with a built 400 sbc 454 tbi and 350 injectors. I just build it and put it in and to feed the 400 I put a external fuel pressure regulator and a 255lph 100 psi fuel pump. I have it set at about 20 psi and it wont go above that with this fuel pump. With this fuel pump I had to change wiring plug to fuel pump, do you think I may have put wires back wards? The 400 wants more fuel need more pressure.
You are using the throttle body injection correct? The regulator in the throttle body will not let the fuel pressure get higher because it is made to run on 15 psi. If you are trying to maintain the computer then you need to get in touch with Jet Electronics and get the computer redone to accept what you have done. I have done this before for a customer with a 383 stroker and it was a learning curve. The older computers do not like the bigger cams makes them over fuel and then the O2 sensor kicks in and leans it and so forth.