I'm starting to think this whole 10 speed thing is not making any sense ...
my thoughts are along the lines of having too many gears without the return on investment.
Feel free to poke holes in my line of thinking.
Looking at the final drive ratio
4L60E - 0.696, 3rd gear is 1.0
6L80 - 0.667, 5th gear is 0.852
10L80 - 0.636, 9th gear is 0.689, 8th gear is 0.854
Not poking holes, more like filling in holes ...
10L80: ... 4.69 ... 2.99 ... 2.15 ... 1.77 ... 1.52 ... 1.28 ... 1.000 ... 0.85 ... 0.69 ... 0.64 (7.32 Spread)
8L90E: ... 4.56 ... 2.97 .... 2.08 .... 1.69 . . . . . . . 1.27 ... 1.000 ... 0.85 . . . . . . . 0.65 (7.01 Spread)
6L90E: . . . . 4.03 . . . . 2.36 . . . . . . . . . 1.53 . . . . 1.15 . . . . . . . 0.85 . . . . . 0.67 (6.01 Spread)
4L60E: . . . . . . . 3.06 . . . . . . . . . . 1.63 . . . . . . . . . . . . 1.000 . . . . . . . 0.70 (4.43 Spread)
OK, now multiply by a 'reasonable' axle ratio (the often forgotten step!)
10L80 x 3.23: ... 15.15 ... 9.66 ... 6.95 ... 5.72 ... 4.91 ... 4.13 ... 3.231 ... 2.75 ... 2.23 ... 2.07 (7.32 Spread)
8L90E x 3.23: ... 14.73 ... 9.60 .... 6.72 .... 5.46 . . . . . . . 4.10 ... 3.231 ... 2.75 . . . . . . . 2.10 (7.01 Spread)
6L90E x 3.23: . . . . 13.02 . . . . 7.62 . . . . . . . . . 4.94 . . . . 3.71 . . . . . . . 2.75 . . . . . 2.16 (6.01 Spread)
4L60E x 3.23: . . . . . . . 9.88 . . . . . . . . . . 5.27 . . . . . . . . . . . . . 3.231 . . . . . . . 2.25 (4.43 Spread)
If I knew how to better spread those numbers out for a more visually accurate representation, I would ...
Many more underdriven gears that have also gotten more assertive have noticeably improved city MpG (and acceleration).
BUT
Despite more underdriven gears, the final gear ('times') the axle gear, ain't never gonna be under 2 in a truck / suv.
Hence lean cruise, followed by Engine Half@$$, followed by Cylinder Confusion, and highway MpG has improved,
just not by as as much as city MpG.
Note:
3.23 is a decent axle gear for 10L80 or 8L90 (does GM even bother to offer an axle gear besides 3.23 anymore?).
3.23 is passably inoffensive for a 6L80 (GM offered 3.42, 3.73, and rarely 4.10 for heavier and heavier-duty 6L90 vehicles).
3.23 sucks chapped unwiped @$$ for a 4L60E, explaining why GM offered 3.42, 3.73, and 4.10 far more often for heavier 4L60 & 4L80 vehicles.