You must not understand what I said.That's exactly a tire problem. They don't roll quite as well and they weigh more so it takes more power to turn them.
Cruising I can watch the mpg fluctuate from 60-45 and all over in between. 10k miles ago the fluctuation was 57-63 in the same circumstances.
That huge variance is NOT attributable to rolling resistance (a constant). It's a variable. There is something causing the PCM to add and subtract fuel in larger increments. Load isn't fluctuating while this is happening.
I believe I have a dirty or faulty sensor. The tires may drop he mpg a few but they won't cause that.