Low fuel pressure

Hi I wanna start off by saying how great this site is keep up the good work you guys have helped me out many times. My car started having starting problems and hesitating problems. I was for sure it was a faulty fuel pump. I replaced it and it did exactly the same thing. It is supposed to have between 40-47 psi with the fuel, but it only has 32. I also checked the fuel injectors with an ohm meter, found 2 that tested low so I replaced them thinking I solved the problem. Of course it didn't. Fuel filter has been replaced. I am just curious what else could cause low fuel pressure? I am thinking fuel pressure regulator. Also I had a check engine light the code was 33. I have no mass airflow sensor I thought maybe it could be my MAP sensor so I grabbed one off my buddy's car a 1996 Monte Carlo 3.1 and it plugged up the same but didn't make a difference. I think it is just a faulty brake pedal switch because my brother was driving it and it looked like my right brake light was out but when he got back it was working so maybe it just stored that code when that happened. But there is my problem any help would be appreciated. Oh also how do you test fuel pressure regulators. I heard you start you engine and unplug the vacuum line and it should jump up a little in PSI. There is no gas in the vacuum line. Also pressure seems to not increase when you rev the engine with the fuel tester on it. Or get pressure when you turn on the ignition but I still here the fuel pump. Anything helps, thanks.