I have a 08 Ram 2500 with 17". I carried a truck camper and needed added rear axle capacity. I went with the 285/70R-17 and could not be happier. If you are going to upgrade the 285s will fit nicely and are not too much taller. They should not affect your speedo too much, just check it with a GPS (I was about 2 mph off, hardly a difference). I like the Nitto Terra Grappler/Toyo Open County A/T for their tread life, traction, and carry capacity (3750 lbs). Just something to think about.
Head over to cumminsforum.com/forum tons of specific info for the Dodge crowd!!