Chasing Knock Retard Like A Fart In The Front Yard--Possible Low Fuel Pressure?

[Brando1118Burb]

Hello,
This is my first tune and my first post.
I have a 2003 Suburban 1500 2WD with an LQ9, slightly shaved 243 heads and the GM Hot Cam kit 219/228. Got a highly modified 4L60E behind it running a brand new True Trac rear end. I'm running the 33lb injectors as this was a Flex Fuel truck, but now it's just straight E10 93. All injector data is correct as it was pulled from a stock tune. I imagine my static compression ratio is ~11:1. I expected to pull some timing with this set-up, but I feel that as I got to 19 degrees WOT and the histogram showed I was still pulling 6 degrees of timing, that something else possibly could be up. I also ran some octane booster (Lucas) with ~10 gallons and I was able to have an almost clean histogram with only pulling 1-2 degrees of timing with 24 degrees in the WOT area. So obviously this knock is the real deal.
Next I checked my fuel pressure:
Key On/Engine Off: 51psi (repeated a few times)
Engine idling: 45 psi
I feel I may have found my problem, but I would like to run it by this forum first as I have learned an incredible amount from the generous folks here that give their time to this as a hobby and as a profession. It has been a lot of fun and I sincerely thank you all for helping me get this far.
Is this fuel pressure acceptable? From what I read on line I should be in the 60psi range KOn/EOff and over 50psi with the engine idling. When I give the truck a little gas in park, the psi drops to the early 40's.
Got a AC Delco fuel filter on order to be delivered tomorrow from the 'Zon. Maybe that's all it is.
Fuel pump is OLD. Truck chassis has almost 500k on it and only has two fuel pumps under its belt. Injectors have 90k on them.
Not sure how to test the regulator, but the truck runs fine so the regulator theory is a long shot.
I don't see where I can attach my tune and log file. Might be because I'm a newb.
Thanks all for any guidance.
Brando

[cobaltssoverbooster]

58 to 62 psi is the range you need. Dips are normal but not that low. If the filter doesnt help, replace the pump. Walboro 255 or aem 320 in tank pumps are the typical go to's.

[cobaltssoverbooster]

By fix I mean fuel pressure not knock. There is a chance other things are happening but stable fuel supply is a must.