I sadly don’t have a scan tool just yet, but I will do some testing when I do get one.If you have no scan tool, try disconnecting each individually your coolant temperature sensor, your intake air temperature sensor, and your MAP sensor. Disconnecting the sensor forces the PCM to use the base map with no modifiers. Maybe you'll get lucky and simply find a failed sensor. It doesn't seem likely but I can't think of anything else that could improve after warmup; Once conditions are met to use the O2 sensor in closed loop, the PCM corrects fuel as necessary so you need to test while quite cold.
I’ve replaced the coolant temp sensor twice, but I’m not a fan of shotgunning parts at it.