SJC...Had you typed the code in correctly back when...I'd have found it on my search.
P0171 Lean Bank 1 aka front sensor is telling the PCM to adjust the fuel ratio outside of it'* "normal" range.
Pull your negative cable off the battery and look under black boot...any corrosion?
So far..I have done
Cleaned battery cable at both ends....and I mean..dremel tool wire brush..then contact cleaner clean.
Also cleaned the ground on the back of the engine next to the oil pressure sensor.
Pulled the wiring conduit off and ensured a good connection at S110 (that'* a splice 4 inches away from the alternator)
Replaced loud fuel pump, strainer and filter
Swapped injectors out with a perfect flow matched set
Replace vacuum hoses...every single one
Pulled regulator and checked it.
Sprayed engine looking for vacuum leaks
Cleaned bottom of ICM/mounting plate
Cleaned every single ground, body and engine within the engine bay.
All of this started right after I changed the battery and noticed some corrosion on my negative battery cable. My new cable is on order from GMPD and I can't wait for it to arrive...Then I will put it on..clear the code..and watch it come right back on. Pound my fists a little and look for something else.
In other words..yeah..I'm working on this issue for you.