Once you go diesel, you won't go back!
And as to the exhaust brake? GET IT! You will be so much more relaxed in mountains, and probably can stop quicker than with out one on the flat!
I have a 2005 Ram, with auto, 3500, quad cab. It gets a reliably accurate 19MPG empty at 65-70, and 12-15 MPG with my 4000 lb camper. When the camper is off, and I have my 11,000 lb 4 horse, with living quarters gooseneck on, I can still hold 65, and still get at least 12 MPG. with NO DPF!!
The maintenance on a diesel is not more than a gasser, as you don't have to change the oil as often. I use "Oil Analysis", and "Blackstone" says my oil can go an easy 15,000 miles. I do change the fuel filters more often, but I have two filters, and want to save the injectors.