Turbo brake seems pretty damn good to me. I’m about 25-26k loaded down at gross and I don’t have to touch the brakes if I don’t want to. Let that bitch rev, it will slow you in a hurry. I’ve seen 4500rpm without issue. Running down the passes between Durango and Silverton, I’m constantly up shifting and downshifting 1 gear to hold speed. Never touched the brakes. Your down to 15-20mph in some areas for a couple miles due to curves and my buddy with his cummins was burning his brakes up becuase the trans keeps the converter unlocked in 1st and it’s too low enough, 2nd is too high and offers no help in grade braking. My old truck was the same way and no turbo brake. That suuuuucked.
I do agree the 10 speed doesn’t get very aggressive on down shifts for grade braking if you are not using cruise control. It seems to use the same shift strategy of the 6 speed but since you don’t have as large of gear jumps when down shifting, doesn’t work as well.
The plus side is when I’m unloaded and truck goes into grade braking down a hill, it’s much smoother and not overly aggressive like the 6 speeds were.
If you turn cruise control on and let it control grade braking, it does a pretty damn good job at it. You get about 2-3mph swing out of it but I don’t see an issue there.