I'm running a 2019 2500 with the 6.4, 8 speed and 4.10 rear end. Plenty of power and torque for a gasser.
We have an ATC Panther mounted in the back that stays on the rig full time since I purchased back in December 2019.
Combo runs great and stays within the power bands quite nicely. When the MDS is engaged, it does have a tendency to lug when light acceleration inputs are applied. When in tow/haul mode the MDS is disabled and the transmission shifts smoothly with changes in accelerator inputs. Have not experienced hunting for gears, but I suppose that depends a lot on how your drive.
I can't speak to driving impressions with respect to towing as we do not use the truck in that way. We went for the Hemi because we wanted payload (3,200 lbs.) over towing. If you are going to do a lot of towing it's a no brainer, go with the Cummins.
In regards to MPG I have been satisfied, given that this thing is a beast with a 6,800 lb curb weight. Empty on the highway at 1,800 rpm I was getting about 16.5 mpg. Loaded with the camper that's a different story due to substantive increase in wind resistance and coefficient of drag. With a tailwind I get about 15 mpg, headwind fuel efficiency plummets to about 10.5 mpg. In city driving you can expect about 8 mpg.
On flat ground the MDS performs well, when pulling grades you'll want to switch into tow/haul mode otherwise it will lug a bit before downshifting.
I only have about 5,700 miles on the truck at this time, so I really cant provide any long term impressions. This truck is not used as a daily driver and is only used for wandering boon-docking excursions into the field. For our use, we're quite happy with our purchase.
Hope this helps.
2000 2WD Chevy Silverado 1500 5.3 liter V8
2019 Ram 2500 6.4 liter Hemi
2015 ATC Custom Panther Shell
When you come to a fork in the road, take it. Yogi Berra