So I had a 2003 Ram 2500 from 2007 until earlier this year. That truck had the 5.9 Cummins and 6-speed manual with the 4:10 gears. I pulled my 16,000lb toyhauler with it no problems, but I did have to add helper springs in the rear to beef it up a touch.
I traded that truck in my my current truck, a 2009 3500 dually with the 6.7 Cummins, 6-speed manual and the 3:73 rear gears. I have yet to get this truck coupled to the toyhauler, but the whole reason I traded the old one in on this one was to move to a more stable dually platform for my big, large, heavy trailer. YMMV since your trailer will be considerably smaller and lighter than mine.
I put a little over 200,000 miles on my old truck, always kept the oil changed, filters, things like that. I would say, with the old truck, aside from the typical stuff that wears out over time like injectors needing replaced, clutch, brakes, the normal stuff, I never had a problem with that truck. I haven't owned the new one long enough to form an opinion on it yet, but it had 212,000 miles on it when I got it and I did have to replace the clutch already (which was not unexpected). But I find these Ram diesel trucks (in the 2nd gen and 3rd gen at least) to be extremely reliable and long lasting rigs and they tend to pull like a freight train no matter what I throw at them.
As for the DEF comment above, I'm lucky that my 2009 is the 3500, which still uses the 2008 platform so it doesn't have the DEF system on it. 😎
That being said, it also doesn't look like the 2009 Ram trucks either, so it's a trade-off I guess. 🤷♂️