I've got 34k on my 2020 RAM Mega Cab 3500 SRW and will also backup what has been said about the funky shifts from the Aisin when not under load. Never had any issues towing with want for more power or any issues with peformance.
The automatic exhaust brake and gear limit is amazing in any mountain towing situations.
Plan on fuel filter changes (both of them) with every oil change - and oil changes vary based on fuel consumption and not so much mileage it appears given the % tracking of the truck. Go ahead and order the filter tool and the low profile filter cap socket before your first oil change. Its not fooling around with the low DEF warning system, it WILL set you to 5 mph so I have kept mine at 1/8th min tank.
If you get the dealer option B&W gooseneck hitch, and hopefully they have fixed it because there was a recall about it... MAKE SURE the lever is all the way seated for the pin. Theres a point on the pin and if the ball isn't seated in the receiver, the tip of the pin will go in and the spring will draw the lever in but not quite as far as it should because its not a 1:1 linkage. The trailer can yank the tip of the pin off and thats just a mess.
Also, I hope yours got the cargo monitoring because it would be great for hooking up a gooseneck one shot by yourself - I tried to add it to mine after the fact and the harness isn't even in there and its not worth ripping the headliner out to add it.
As for the comments on the twin airmattress, you can fit one in there if its inflated while its in the cab. Its deformed some and if you're 6' you can sleep at an angle like mentioned. I used to do it in my OG '06 mega all the time.