Not my trucks but here's my experience.

I've driven 95-96 Ford F450's with the 7.3L Power Stroke with 6 speed and couldn't kill them. I pulled loads up to 26K gross and while slow it pulled the load.

I don't remember the year (Somewhere between 2000-2003) but have also driven a Dodge with the Cummings and 6 speed pulling a 45ft 5th wheels trailer. This truck impressed me, I was able to maintain 65 mph up hill with the trailer lightly loaded. I also drove the Dodge empty at highway speeds (60-80 mph) and got 20 mpg!

I prefer a Ford overall but for the price I just might buy a Dodge if and when I am in the market for a newer tow vehicle.