working on a heavy LS1 which went into a 63 Nova convertible. Engine came out of a 2001 Vette, tranny, fuelpump, PCM wiring out of a 1998 WS6.

SInce rails don't use a return line we put in a fule filter with intagral regulator from a 2001 Vette.

However, I have 85 psi at the rails instead of 58 like it should be. Changed the IFR tables to match it but I am curious where the heck that high pressure comes from !

 

Have you checked your fuel lines? Sounds like you might have some kind of restriction in the return line.