MPG with late model Ram 3500 with 4:10 carrying TC.

We have a 2014 Diesel DRW Aisin 4.10.
Last summer over 2 months loaded with 4500+lb TC we averaged (hand-calculated) 11.7 MPG driving over 13,000 miles from northern VA to Inuvik, NWT and all the usual routes for an AK/Canada trip.
Going west at 75 mph through SD on the interstate against the wind we got around 9 MPG, ouch. Our mileage includes lots of 15-35 mph gravel roads.

I have a 2015 Dually 4wd with Aisin and 4:10's. to answer your MPG question, it all depends on your RPM and load and city/highway.

running 70mph on PA turnpike with 990 loaded and towing a 7x14 v nose trailer I see around 10mpg but this low number is because of the RPM I feel.

Running Rt 13 down through the Delmarva Penninselia towing a 4000 lb jeep liberty 55/65, this is with a red light every couple miles, I can see 12-13 mph if I am not in a hurry.

Now that truck with the Aisin gets you the Highest powered Cummins they produce for that year. With my 990 loaded and towing the jeep, when the light turns green I can accelerate with traffic with no problem. (in fact it will take off faster them most people at a light with no problems).

And the tow/haul switch works very well. Rolling along 55 and the light ahead of you turns yellow, just let off the throttle and truck will slow down enough it almost needs brake lights to come on. The exhaust break will hold down to around 20mph.

But yes the 4:10's might be more than enough. I ordered my new truck with 3:73's to lower the RPM some on my frequent 200 mile trip on the PA turnpike.

What is the HP on new Dodge?
New engines are monsters, so I guess Dodge as usually is just a step behind Ford ;)
My 2017 F350 DRW with 3.55 differential will pull truck with 6000 lb camper, or 7000 lb cargo trailer on all California grades without dropping from overdrive.
When empty, I drove 20% grade ... on 4th.
MPG in my footnote.

I have a 2006 in Laramie and the leather is almost as good as the day I bought it 12 years ago. Never parked indoors, or even in the shade for that matter. Love the heated seats too.

Have you considered the manual tranny. I have the taller rear end gears and rarely have to shift down from 6th even climbing mountains with a GVW of over 12,000 pounds and running 19.5's with 34" tall tires. When I do down shift to 5th, it's because the road speeds are 55mph or less on the twists and bends while climbing.

Manual makes for good speed control on downhills too.

Laramie leather is cheap I've heard...vs Limited or longhorn.
Mileage? About the same. 4.10s will hold 6th more, but that makes no difference. 6th is an empty cruising gear, except with deep gears like you're looking at.
Won't help mileage much. Check your mileage in 5th and 7th at say 70 mph flat road. Shouldn't be much differnet.

Regardless of gears, a TC and a light trailer isn't at the upper end of any new diesels capacity. But you're correct, 410s will make it even easier.