At what RPM is the power dropping off at? based on the cam and heads you are running your intake may be part of your problem,a Performer RPM or Weiand Stealth would be a better choice than the Performer you have which is making its power from off idle to 5500 RPM.The standard Performer works well with a cam of lesser duration to improve mileage and low end torque.As for the fuel pump SBC performance pumps are priced reasonable so changing it would not be a bad investment anyway.