Still very early on the new cummins. Early reports are saying good fuel mileage. Some who have recently bought our on the 2013 ram forum. I also recently posted there links I found to ram's build site.
The urea is actually an advantage. Cummins has been using them on some engines for a couple years, so you shouldn't run into any major issues. The big advantage is it lowers regen, which means better fuel mileage, and less restrictive exhausts. You also gain cleaner oil, longer time between changes.
They have been doing the DEF (urea) injection for a couple of years on the chassis cab models. I've also heard it cuts back on regens and improves things overall.
I don't know how many miles on your 2003, but the 5.9 common rail is a really good engine. If it just came down to the engine, I'd say stick with what you have, but I think the new trucks are better overall. Keep in mind, that you have to get a 1 ton to get the Asin transmission also. You can do this with a single rear wheel also if you want.
2004 3/4 ton Quad Cab, 24 valve 5.9 Cummins