Fuel pressure drop

[DRJDVM's '69]

Changed from carb to Holley EFI in Dec 2021- had some stumbling issue and some pinging when I tried to jump on it…….roll in and it was fine. On the data log it looked like I was getting a drop in FP based on the way the car was acting- installed a FP sensor so the EFI could monitor the actual number and confirmed that I was getting an intermittent drop on FP. Dropped the tank, pulled the pump, and sent it to Aeromotive- they stated it was slightly out of specs, so I paid to have them rebuild it. Inspected the in-tank fuel filter and it was clean. Re-installed everything, new fuel lines, made sure all my wires and grounds were good. Did all of this toward the end of 2022 and the car ran fine but I didn’t beat on it, with the plan to get it remote tuned in 2023. If I take it easy, the car seems to run fine.
Did a remote tune with Andrew Borodin and I’m still getting some pinging when I am at lower RPM and jump on it and randomly it will stumble and sputter and the AFR will go crazy. Happened mostly after I got on it and then go back to cruising. Data logs show I am still getting weird drops in FP. Other times its rock steady around 63 PSI.
So, I’ve got some fuel delivery issues, but I’m not sure where/why. Pump is supposed to be rebuilt and good to go…. New regulator… new fuel lines (would prefer an 8 AN supply but I was trying to limit the number of adapters to make that happen). So before I just start to throw parts at this, I was looking for some input on narrowing down the cause. I’m hoping to retain my current tank rather than drop $2500 on a new tank and pump set up etc. I’m fine with a different fuel pump, regulator etc, but I don’t want to start all over with a new tank design etc.

434 ci SBC, naturally aspirated.
10:7 compression ratio
Around 600 HP
Holley Sniper HOL- 550-1003 Terminator X EFI system
Ricks Hot Rod SS tank purchased around 2005 (no provision for the new drop in pumps etc)- standard vent in tank, no vented cap
Aeromotive A1000 in tank pump- rebuilt around June 2022
Holley 12-889 Regulator/filter- non-adjustable- new in Dec 2021
Fuel supply to TB 6 AN earls braided line (originally had an 8 AN supply but couldn’t find single adapter to have FP sender and step down to 6 AN to attach to TB)
Return is 8 AN with Holley regulator/filter mounted back by tank)
Completely rewired the car with AAW kit in 2004 and its has worked flawlessly. FP is run right off the AAW kit