Full Lean in Closed Loop Operation?

[WithHonor037]

Hey everyone,

Ive got a bit of a head scratcher on my hands and am hoping someone might have some new suggestions or ideas for me. Ive got a '91 hatch with a basically stock ka with an emissions delete done and just the other day apparently started running full lean when the engine is completely warm. I can let it sit and idle with no problems even when the engines fully warmed up but when its taken for a drive (engine under load) it will peak and stay full lean after a maybe a mile of driving. Ive checked almost everything I can think of with no evident issues. Ill simplify by just simply listing everything ive tested and checked out ok:
1. TPS - reads spot on at closed and full throttle
2. Coolant temp sensor - .29 on a warm engine (swapped a new one in just
to be sure, no change)
3. MAF - voltage signal tested normal
4. AAC/FICD - taken apart and inspected (not dirty at all, Im pretty good
about keeping it clean), No signs of an issue. Replaced with new gasket.
5. Vacuum Leaks - ran engine at idle and sprayed all intake components with
carb cleaner, no change in idle.
6. Fuel Pressure - fuel pressure stayed at a steady 39psi.
7. Valves - Pulled valve cover and inspected for sticking valves, no obvious
damage
8. Spark Plugs - Pulled all 4 and all were white tipped so all 4 cylinders are
running lean, replaced with brand new plugs and checked gapping
prior to install.
9. Distributor/Cap/Rotor - All were replaced with brand new units within the
last 6 months. Double checked with timing light just to be sure and is
firing right where it always has.
10. O2 Sensor - Have a narrowband hooked to a relatively new Bosch sensor
for monitoring the engines operation (don't tell me theyre terrible
and shouldn't be used for tuning. I know. Its merely a diagnostic tool)
AFRs are normal until engine gets fully warm after driving and then
runs a steady 25.5 (max of the monitor) on accel, decel, idle, etc.
until the engine cools down.
11. Cooling system - Havent checked the pressure or anything but its full and
shows no sign of overheating at any point
12. Oil - No coolant in oil, its dirty, but that's about it

Im sure Im missing a few things I checked but Ive been at this thing for 2 days now and cant seem to solve this. I even desperately tried what appears to be a homemade consult cable to an adapter board. Got it to connect to the ecu using ECUtalk software but it wouldn't display any realtime data. Any suggestions are welcome at this point. Hopefully some of you are smarter than I am! Thanks in advance!