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@$$, followed by Cylinder Confusion, and yet highway MpG improves, but not as much.
Note:
3.23 is a decent axle gear for a 10L80, an 8L90 (does GM even bother to offer any other axle gear?)
3.23 is passably inoffensive for a 6L80 (although GM offered 3.42, 3.73, and rarely 4.10)
it sucks chapped @$$ for a 4L60E (which explains why even GM offered 3.42, 3.73, and 4.10 far more often back then).