I have a PO171 lean mixture, bank 1 code.
I have had MAF sensor replaced twice. Check engine will come on and sometimes shut off. Mostly on. Under hard acceleration, engine pulls strong (235,500 miles) but near redline there is a slight hesitation. Almost like engine not getting enough fuel. IDK for sure. I take excellent care of car and engine. Synthetic oil. Intake gasket replaced, as common problem with 3800's. I use 89octane, sometimes 93. Problem seems slightly better with 93. I'm guessing low fuel pressure or vacuum leak.