pid and parameters for fuel pump duty cycle?

I am diagnosing a P0087 low rail pressure issue with an 08 LMM truck. Truck will certainly hit 26ksi rail pressure until you get to a certain flowrate and then pressure wants to drop to 20-22ksi. Even in WOT testing, the pressure will drop but as soon as throttle is pulled back a bit, pressure will come back to full 26ksi.

Filter replace, fuel line fixes have already been done, vacuum test on fuel inlet shows 4" at idle and 8-10" at WOT, bottle test on the FPRV shows no leakage at all.

I am getting ready to start examining return rates to determine if this is a fuel supply, pump, or injector issue.

I would like to look closely at the pump duty cycle as this will have a big bearing on what the pump is trying to do. Normal parameters for idle and WOT? which PID is it? I am recording gm.frpcom. It appears to hover 40% at idle and reduces to 14.1% at WOT. I am understanding the values are inverted though so a 40% duty cycle would be on 60% of the time. However, that value looks very concerning for idle!