While a new trans may help empty highway driving, when pulling heavy those ten speed trucks are generally in sixth or seventh anyway, with seventh being direct. My Aisin stays in sixth, second overdrive the vast majority of the time. The new HO Cummins is just harder on fuel. I think they ventured too far off the path by running different compression ratio, turbo, etc. versus the Std. There were never so many mechanical differences between the Std and HO in previous generations. I don't care about being a minute slower up the Ike, but 6 mpg on the mpg loop is atrocious. Semis grossing 80,000 lbs do better than that, today. Ram/Cummins had better wake up.
Pulling the same toy hauler, my HO is only 2 mpg better than my previous, totally overloaded 6.4 Hemi, which also had 4.10s and a six speed. That's sad.