are you sure that the problem is the fuel pressure?

you don't say whether you have a pressure guage. if your wiring is poor then the pump might not be getting full battery voltage when its under load (i.e. when the reg is fed pressure from the manifold) thus low flow rate be interpreted as low pressure.

you can test the wiring by connecting a high power light bulb of 100 watts + (depending what pump you have) across the pump connections and seeing the voltage drop from the battery + to the pump +. it should be less than 1 volt if all is good.