Transmission Issue galloping between 39 and 43 mph on level ground Advice

[kdmath]

This is my first diesel (purchased new) 2020 Ram 3/4 ton. I took it to the dealer at about 36k miles because when holding a consistent speed around 40mph the truck was not smooth but more like galloping as the mechanic said. My service manager said the transmission was fried, that three clutches were burnt. The installed a new transmission but didn't determine what caused the failure. When I got the truck back it was doing the same thing. I took it back to the dealer and they called me and said, "we can feel what you are talking about but don't see anything wrong, some vehicles are made to feel, and you need to adjust your expectations." Now at 49k miles I have a trip planned to central CA to pick up a mare and foal and don't want to get stuck on the road so I took it back to Dishman Dodge and they still can't find a cause and the transmission appears ok at present. With the same symptoms I'm very concerned it's a matter of when not if this trans get cooked. My service adviser said my warranty doesn't extend past 5yr (about now) because "I didn't pay for the new trans".
Has anyone else encountered uneven 4th gear?
Any help would be appreciated.