Just as a heads up, Ford isn't using the 7.3 Powerstrokes or NAV DT444 . They switched to a smaller displacement engine. As far as brand loyalty, the cummins are great engines, but Dodge do have weaker trans then chevy. I know the chevy 6.5L was a dog, but I have heard good things about the duramax. And with the allison transmission bolted on, it is pretty bulletproof.

Of course whatever you go with, the heavier the suspension the better. And when you go shopping, tell the sales people what you are looking for, they should let you hook up to your trailer and give it a shot up a couple of hills. Take it out on the highway and give all the trucks you are looking at a good head to head comparison.