P0171: LT fuel trim high but ST looks good

[DrRadar]

I have a nagging P0171. No SES light but the code is there. I haven't had it inspected because two shops have told me it won't pass inspection with a code, even if no SES light.

Originally had high STFT values. Replaced bad vacuum hose. Found vac leak at supercharger gasket; tightening s/c bolts seems to have resolved that. STFT went to about zero and I thought my issue would resolve. No dice.

Live data while driving shows the short-term fuel trim hovering around zero but the long-term fuel trim is +13 to +16. Even after resetting the fuel trim, the LTFT increases back to +16 in short order. The engine is running fine: no concerns with acceleration, fairly smooth idle. I took it for an hour drive with my son watching the live data. Event LTFT looked good most of the time; would jump up if I accelerated hard. It appears LTFT goes up at idle.

Cleaned MAF with Mass Air Flow Sensor Cleaner spray.

Fuel pressure is 40psi but drops quickly. I think that's because there's a leak at a swivel connection with the gauge rather than a problem with fuel supply. (If I disconnect gauge, charge it, I get a good squirt when opening the Schrader valve.)

Disconnecting MAF sensor does not clear P0171 - just adds P0102.

I'm at a loss on how to proceed other than to methodically progress through service manual steps with possibility of replacing upper end gaskets, more hoses, etc. Suggestions greatly appreciated.