This is good food for thought for me. I have a new fuel filter and newish fuel pump and still can't kick the P0171. I also have fresh plugs!What's interesting in your case. Is only the P0171. Even though I suspected fuel starvation. Typically I'd look for both bank 1 and 2 (P0171 & P0174) to indicate a fuel starvation issue, due to fuel delivery. I'm confident the fuel pump and filter did solve your issue, at least enough. But I suspect you've more to consider.
You said "Fuel injector cleaner (part of my regular PM)". Consider sending to someone like FIS. Also consider replacing fuel pressure regulator, considering mileage and your MPG drop.
When to Clean or Replace fuel injectors
Please post your experiences and thoughts on the subject. I’ve been considering cleaning or even replacing all 8 fuel injectors, is this wasting time and money. I understand keeping fuel injector clean by adding a can of additive to the gas tank, now & then, is a good practice. This keeps them...forum.ih8mud.com
I did not see you mention spark plugs.
Ticking time bomb TICK TICK TICK: Spark plugs Alert Alert Alert!
TICK TICK TICK POP POP POP is a ticking time bomb, often mistaken as exhaust manifold crack or gasket leak leak. ALERT, ALERT, ALERT: Spark plugs are working themselves loose. "Walking Out" Then blowing out of head, taking their female threads of head with them! Very damaging! You think TICK...forum.ih8mud.com