Volvo Penta 5.7GLI Fuel Pressure
 

I have a 1997 four winns with a 5.7 gli, throttle body. The boat stalls out when you give it gas. The engine only has 12lb of fuel pressure, I changed the high pressure fuel pump, located at the back of the motor, and I still have only 12lb of fuel pressure. I'm guessing I need to change the fuel pressure regulator but I'm not sure, I don't want to keep throwing parts at it. What else could I be, what should I tear to find out what's wrong