These transmissions work so well in the modern cars because of how integrated the controls are into the whole car. We have an 18 Durango R/T and I really like the how the 8 speed works but I think it would be really hard to do from the aftermarket.
Its just a tune you put into them. Not sure if the 8-speeds are ZF tuned or FCA tuned, I know FCA has had troubles with their own tune in the ZF9 (FWD) used in the jeep cherokee with harsh shifts etc. Word is they called up ZF to help and now its fixed. Either or, it may work with a base tune from 6.4 car or the aftermarket can tweak it from there. I don't think it'll be too difficult.
