That is very interesting.

https://en.wikipedia.org/wiki/ZF_8HP_transmission

With “potential” 3.7 first gear and 0.64 overdrive maybe even 2.76 diff ratio could be used up to 1% grade hills on Interstate cruising.

Gotta take it on faith that

“ One of its main aims is to improve vehicle fuel economy, and it can achieve 12% saving compared to the ZF 6HP transmission and 14% versus modern 5-speed transmissions.”

as those internal trans gear friction reductions “boogle my brain”.

I suspect they are “wrapping in” fuel economy improvement due to lower engine rpm and wider throttle opening