I'm thinking it was starving, but probably not due to a calibration fault. I noticed when I shut it off I could hear the pump running quite a bit longer than usual. It occurred to me this morning it was probably sucking air (the fuel gauge has been reading near E for a day or two). When I peeked in the filler cap I could plainly see the pump's filter sock, and it seems like the pump might have popped out of the bracket. The y-body fuel tank design is one thing GM solidly botched.
After adding a few gallons and re-priming the system, cold start at 6.5c popped right off. So the O2 shift I mentioned on both sides may be invalid due to air in the fuel system.
My stock bin had this for the 12df2 table:
Very interesting find.Code:20
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This is referred to as Tau in the Banish stuff I have.