Fuel filter & PSI test on the pumps like Dominic says.
The original owner of my car never changed the F/Filter, okay so he only did 7400 miles, but over 14 yrs. I r&r'ed it and the gas was orange that came out. I do it every yr now...maybe a bit of overkill
Remember that upon cold start both pumps run. Secondary pump shuts off after 140*(?) water temp is reached. On a warm/hot restart I think the secondary pump runs for a programed time limit, but I'm not 100% sure on that fact. KOEO pump test could be useful.
I know I swapped out my original pumps just this year just because they were 20 yrs old and I know they were testing at the lower end of the FSM acceptable PSI limits during the KOEO test.
When she acts up have you given a sniff to the exhaust? Does it smell rich or lean? I know the code says lean, but can you smell it? Did it make your eyes burn?
The time period description you give makes me want to say something electrical....you know as it heat soaks the issue gets worse. Generally that's what your symptoms seem to be saying. JMHO. Run down the pumps & filter, next I would look at checking for battery & alternator condition and then the ignition system condition, then the injector coils electrical condition.
Keep us in the loop and good luck!
Tom