This has been covered a few times here. Ram hasn’t done the 8 speed in an HD because the parking paw is not rated strong enough to hold a truck & trailer to rated capacity on a hill. This makes sense since the trans was not originally designed for a truck. Hopefully they can find a way to remedie that as it would be a great improvement mileage & towing for the HD gassers.
BTW I’m a transporter towing TTs & boats with my ED. 485 TQ 390,000 miles so far. Have taken to 15,800 CVW up & down 5&6 percent grades. It has weak transmission braking but it works well with a turbo brake to hold speed when descending grades.