Today I just installed a walbro 255lph intank pump for my 2004 returnless fuel system silverado. I am running a sts fmic and have noticed at 5psi,the higher the truck gets into rpms the more the fuel pressure drops off. truck idles at 60psi and at wot drops down to 58psi then down as far as 55psi in the higher rpms. pretty much doin the same thing as the stock fuel pump did. Is this right? I also tried running 10psi and it drop down to 50psi and I let off the pedal. Any help? Thanks Thomas

 

some drop is normal. Mine was dropping to ~57lbs.
I installed a Magnavolt fuel pump booster to increase fuel pressure in boost.