1993 Buick Century Wagon 3.3L v6 Fuel pressure problems.

[FAITHFULMAN]

I am having a problem getting my 1993 Buick Century Wagon 3.3L V6 to give the book listed pressure. I get 18 psig when the book calls for 30-44 psig with the vacuum hose on the fuel pressure regulator attached.
I have replaced the fuel pressure regulator, fuel filter, fuel pump screen, and the fuel pump. I have also blown out the gas lines with air and inspected them for kinks and leaks. I had lower pressure (5 psig) before I replaced the fuel pump, but now I only get the 18 psig. The car will drive like this, but is very slow getting started from a stop. I personally can't think of anything else that would effect the fuel pressure and the book doesn't point me to any other components to check. Help is greatly needed.