Sybil and Vortec Dave

Sybil. Still confused.  For the record, I did buy "the book," but for the life of me I can’t find the direction I need to figure this out.  Several of my issues first reported under topic “Vortec Dave” almost 2 years ago have been cleared up.   I take issue with folks that think 17mpg is good for my vehicle, but please read on.  Long winded as it may sound, I could have added tons more info.   1997 K1500 5.7vortec  (L31) Silverado Z71, 445,000 miles, and also for the record I now can reliably get over 20mpg on the hwy (21.7mpg several times now.)  But city mileage still sucks. It also goes through a ton of oil (I’m thinking a guide not a ring)  but I haven’t done a leakdown yet. Got a knockoff Tech2 and got cam retard to 0.  I have a worthless Innova but all that’s good for it fuel trims and simple PID info.Issue 1:  LTFT seems to CYCLE around (beyond the “normal” 4.7, 0.0 (B1, B2) condition where I have a native B1 lean (which I can live with) which is probably from a valve, and this has been there since I redid my heads several years ago- I lapped my valves to not be super tight so the compression wouldn’t suck the rings out. Again, I’m getting over 20mpg hwy…..The “cycling” will go from the (4.7, 0.0) on one day to (6.3, 1.6) the next to (7.0, 2.3) the next (and betweens), and clock around again to (3.9,-0.  and you can feel the engine missing when  it goes too lean (ok, too much richening response), yet the ecu (“Sybil”) doesn’t seem to recognize a good thing when she sees it, because it purrs smoothly at the B1 3.9 to 4.7 level, and she just keeps clocking through it until it goes rough and rich.  My theory is that there is a sensor short somewhere that is sending Sybil conflicting signal data and she just goes into teenage “whatever” mode (or some kind of “I have no response to that” algorithm.)  Issue 2:   MAP values normally 10.6”Hg but sometimes out of the blue they’ll go to 10.3 for a bit and sometimes 10.9 (sometimes at the same stoplight.)  Is this normal?  I bought a rockauto cheapo years ago and tried that, and a few months ago swapped in an older OEM MAP sensor from pickapart, and just in case something fried the last one, I just bought a new OEM GM unit but haven’t installed it yet until I know if a surge/short is frying them or something.   I test MAP and MAF vals at idle because it doesn’t seem to be a cruising thing…Issue 3:   If I drive up to elevation, say 7000’ (from my normal 500-1000’ home range) the next morning the exhaust will be smoggy smokey rich, the LTFT will go to (10.4, 3.9) or thereabouts.)  When I drive with a heavier load, especially up grades, the LTFT’s (at idle…) will be richening + again also, but when I get back home, after a day, I’m back to (3.9, 0.0) ish and clocking through the values again. It sounds like this should be a goofy MAP thing, but at this point, who knows.      25 years, 450k miles, I have replaced most things as they went bad.   I have replaced main battery cables,and tested most circuits, and have replaced pretty much every component and sensor at one point or another trying to dial this crap in. MAF is usually around 0.8#/min (in range at idle.) I have rebuilt the MPFI injectors, including testing resistance, etc.  My fuel pressure is spec, so not the  pump or rail, or regulator.  Redid exhaust manifolds, Y-pipe/cats, all that.  Changed out intake to nice one from pickapart (and had my head shop guy resurface it,because some dufus said there was a GM head /deck flaw causing leaks, and my B1 lean was probably that. Nope.)   I tested the different sensor signal voltages but don’t have any specs to see if something’s off.  I tested 5v ref and it seems right, but don’t know whether “spec” is 5v exactly, 4.9, 5.1 or what.  Since I’m getting over 20mpg on hwy I know I’ve got some things fixed.  I even divorced Sybil a couple months ago and installed a new ECU, thinking I had finally exhausted all other possibilities. Not!  No change, but don’t tell her lawyers.  When I test the 12+ voltage at the EGR or MAF, I’m reading less than battery voltage but not by much, but I note fuseblock voltage is spot on battery voltage, so there may be a sink somewhere, the question being, is a fraction of a volt enough to cause the sybil cycling?   If I knew what the 5v ref voltage spec really was and if it matters, what line voltage is supposed to be in the “pink” 12v+ wires, maybe that would help me chase it down.  Should sensor 12v+ voltage be equal to the battery and fuseblock voltage?  Only thing left I can think of is a chaffing of wires somewhere (like exhaust manifold) sending a wildhair signal to Sybil somewhere?   Any help?