Q: Leak down test confusing me

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after low power hesitation and poor mpg, a very lean condition was found (fuel trim +20-+25 but even in both banks, so not an injector issue) did a fuel pressure and leak down test. Fuel pressure was low(under by 10 psi) and after the pump primed and shut off almost immediately the pressure started rapidly dropping. almost as much as 1 psi per second. I pinched off the return line to determine regulator or pump. When pinched, the pressure jumped up to almost 90 psi but then just like the original test began falling very quickly. So not the regulator clearly, BUT the pump obviously has sufficient pumping power due to the high pressure when return line was pinched. So that makes me think fuel pump check valve? And if so would replacing the entire pump assembly fix that. I was expecting to to pinch it and see either A-pressure sky rocket AND hold (regulator) or B-lower fuel pressure and then constant drop(pump) so some direction here would be wonderful

My car has 150000 miles.
My car has an automatic transmission.

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