Congratulations on your new truck! I have a 2015 Ram 2500 CTD that I purchased new. I just do oil changes and fuel filter changes (there are two fuel filters) and the only time that I've ever used any fuel additive was when I got hold of some fuel with water in it, otherwise it doesn't need anything.
The cheapest place I've found to buy DEF is WalMart. I always use my engine brake and I have 92k on the truck with about 60% left on its original factory brakes. As for dependability, your old 6.0L isn't even in the same league as that Cummins. It's a super dependable engine with an amazing amount of power when towing.
