That does not logically follow. The five speed automatics were all bad to terrible, but the six speed automatics have been doing very well. I have a few clients that operate vehicle fleets for construction or oil field services and it is exceedingly rare for a six speed box in their service to not reach 250K. Of one company’s fleet, I can think of only two of eighty trucks that didn’t and one of them was destroyed in a collision. One actual failure out of eighty over 250K is actually better than the older four speed automatic trucks did.
I'd like to see posted failure rates on transmission from all manufacturers. But that info is surely kept form the public.