Just remember that the CTD engine is a lot heaver that the 6.4/5.7 Hemi. Payload on my previous 2017 RAM with the 6.4 Hemi was 3020. My current TV is 3739. I tow a 12K gross fifth wheel, and honestly, it tows a lot better with the 3500 - ya the diesel is a big part of that.
Check around, the 3500 is not much of a jump in price and you should be able to get a god deal on a 2018.
The other plus with mine is that I can easily upgrade to the next bigger fifth wheel in the GD Reflection series which may be the plan after retirement and it will only be the two of us.
I'm not in the camp that looks at axle ratings, although I have seen some 3/4 ton trucks pulling way bigger rigs than mine. Maybe it's true about manufacturers deflating the ratings - but the only info you can get on that is on a RV forum. Not saying I want to argue about it.
Another thing - published numbers are all over the place. Your best bet is to buy the truck you want, and then take it to a Cat scale and get it weighed - google Cat scale locator.
Good luck.
