Opinions on Fuel Pressure Readings

[TX '90 ZR1]

I had noticed the cranking time seemed to be longer than normal at times.
Decided I should check fuel delivery. (Injectors were changed about 3 years and 4000 miles back)
This is what I observed with fuel level @ 1/3 full.
Turn key on, pressure to 21 lbs (WAY low!) and then starts to bleed off. Goes to zero pretty quick. Start cranking & pressure to 42 lbs and a steady 42 @ idle. Take vaccum away from regulator and have a steady 51 lbs. On shut down pressure bleeds off.
Took car out to check drivability. Generally OK, but did stumble a couple of times @ WOT. Did not seem to quite pull as strong as it should.
Filled tank as it was getting pretty low after the drive.
With tank full, turn key on and get 42 lbs and then a bleed off. Pressure will drop, sometimes hesitate or stop for a few seconds, and then continue the bleed down.
Idle pressure still 42 lbs & 51 lbs w/ vaccum pulled from regulator.
Do not know if the pumps have been changed. I'm suspecting a leaky pump check valve? Filter was changed less than 200 miles back w/AC Delco unit from Jerry. Opened old filter and it looked fine inside. (No rust, etc)
You guys and gals think I may be on the right path?