Tow Vehicle for 10k bumper pull

One consideration, look at the 2019 leftovers, all the manufacturers are offering incentives, often with zero interest. You can find new Ram 2500's for under $35k with some searching.
edit add, just looked, up there the few left are around 38 and up.

I agree any of the current or newer 3/4 ton trucks should do the job nicely, particularly since it sounds like you won't be towing often. We have towed our TT TH that weighs over 10K# when loaded with toys and water for over a dozen years with our Chevy 3/4 ton gasser here in the mountain west, we live and mostly camp above 6K' elevation where a gasser loses 3% power per 1K' elevation.

Even so, we don't have any issues letting it roar into it's power band (above 4K RPM) when climbing, has nearly 100K miles and no issues with tranny thus far. Of course it sure gets thirsty, just filled it up @ $1.12 a gallon which made be giggle when I remember many moons ago we paid up to $3.80 a gallon toting our kids to all the national and state parks in the four corner states.

For your viewing pleasure, no load leveling or sway controls needed. ;)

I agree a modern 2500 would be adequate (but sit tight, I'm sure the DRW crowd will be here shortly). As for which one, of course it's a constant debate. I own a 6.4 Hemi and you are correct that the tranny sucks. Aside from shifting poorly and having terrible gear spacing mine has blown up twice before 100K miles. This being said, when I shopped I found I got more for my $$ with Ram.

I think any of the trucks will do the job and it really just comes down to which one you like best. I'd have no problem with any of them. Since it sounds like you won't be towing often a gasser is probably sufficient (I should have mentioned earlier that the DRW diesel crowd will be here shortly).

Weight wise a 3/4 will do it but at 40 feet I'd get a one ton. That's a bunch of tail for a dog to tow.