For a little background. I bought this truck(1993 f150. 5.0 225k miles) as a temporary way to move. My daily decided to crack its head so the truck became my new daily

My current issue is throwing me for a loop. Drives great when it’s cold. Get a mile or 2 down the road and when slowing down or the RPMs drop too quickly it’ll want to stall out and occasionally will completely die out. Has long tube headers and no cats. Can audibly hear it misfiring while it’s recovering from its stalling. Won’t throw a check engine light or any codes

now for my list of maintenance.

Rebuilt factory heads
new EGR / EGR tube
new plugs. Wires (routed correctly) rotor and cap
cleaned throttle body/IAC. No change. Replaced IAC. Still no change.
new TPS. Purge valve
new rear tank (front doesn’t work) pump. Filter and rebuilt OEM injectors
replaced any damaged vacuum lines (smoked tested the system)
Took the ECU apart and discovered the board inside was replaced. sharpie dates it to 2016
removed SMOG pump and blocked off ports in the back of the head
I’m sure there’s a couple other things I’ve missed that I’ll remember later. Truck is timed to 10 degrees BTDC.

Fuel pressure is at spec. Occasionally once it stalls it won’t want to restart for a couple seconds it’ll sit there cranking

it did it in my driveway one day and thankfully I had my fuel pressure tester on me. 35lbs of pressure while cranking and it took about 20secs for it to fire.

any ideas? Starting to scratch my head a little bit.