starts but dies immediately

[HTX86chevy]

5.3 DBW and 4l60e into 72 c10 with Factory tank.

This is my 1st time doing an LS swap.
reworked harness myself using guide from (Brenden/Lt1swap.com)
had PCM done by Brenden also.

walbro 255 inline fuel pump

I have added grounds like crazy including 1 to PCM case

I have swapped fuel regulator 3 times and seem to be getting only 52psi on gauge

when I engage the key, I can hear the fuel pump run and stop after a few seconds. I turn the key to on and the engine cranks, starts and dies after 2-3 seconds. no sputtering or anything, just cuts off.

I don't have the OBD port wired up yet.

Any Ideas? what should be my next step?