ls swapped 3rd gen any help would appreciate it

donor truck had return style rails, i swapped it to a returnless crossover and used the same injectors from return style rail (delphi 25317628)
done a little fiddling with it, currently putting exhaust back on. changed flow and offset from 05 truck non flex. should i or can i just drop the fuel pressure and put the fpr reference to vac and change injector back to og?

engine,ecu,pedal ect.. all came from 03 silverado 4x4.
5.3, 218/224 camshaft
4l65 2800 stall
FUEL SYSTEM
walbro 255 intank. factory fuel lines to -6an feed and return.
trickflow fpr set at 58psi. reference to atmostsphere