Sounds like your Fuel Pressure Regulator (FPR) is OK.
You should get around 45 PSI reading with the vacuum line off and depending on your vacuum you should get 32-34 PSI at idle.

I do not know where you seen the 39 & 30 but who ever said it was wrong.
You vacuum may be a little low or your engine was idling a little high.

Most 5.8L engines will did at between 28-30 PSI fuel pressure.

Every one that I have worked on and others I have worked with the above is true and not what the book says below.

ENGINE RUNNING 30 - 45 PSI
KEY ON, ENGINE OFF 35 - 45 PSI

I do not know how they would come with those readings.