Correct, Tracy - the Intake Air Temp sensor part of the MAF was over-reporting the intake air temp, and causing havoc with fuel delivery. It was reporting late spring air temps in early March for that location, and when I asked him what the weather was like, he told me that it was cooler than the sensor seemed to think. (low 70s F vs low 40s...quite a difference). Even Idling in the driveway, there should be no way that amount of heat would creep through the intake tube - it would be melting, and obviously wasn't.
From what I recall from the before and after screenshots of his scantool app, after swapping the sensor out, the throttle angle decreased as well, confirming your supposition about why the MPG was lower than expected/hoped.
he didn't notice it, or wasn't looking for it as the answer, but I was sitting in my car at pretty much the other end of the country thinking how chilly I was when my eye caught that tidbit. A quick convo about speed-density, a test of the MAF (pulling the connector while it was running should kill fuel delivery because it's not meterng air, but it didn't, so it was temperature)...and a quick search of Rock Auto showed that the Delco part specifically stated it measured air temp. Kudos to him for trusting me and ordering the replacement sensor quickly....and the ensuing fuel savings offset the price of the sensor.
BAM! back on track for the groove to do it's thing.
Again, if you're stuck and in a place where something doesn't make sense, ask for help from someone. That's what we're here for, and we're happy to help. #ThisIsTheWay of Gadgetfolk.