If you are in western Canada, forget the Cummings diesel. Many stations don't have diesel, and starting it up at 30 below ain't easy (a son-in-law had one but sold it after one winter). Also too damn noisy. Diesel now is more expensive here than regular, I am told.

Ford and Chevy outsell Dodge by a wide margin here; I can't advise on makes (I prefer GM, no real reason).
Unless you are hauling a heavy trailer, a 1/2-3/4 ton depending on make) should do you.

I had a leased one (3/4, one year old and checked out by a mechanic). Not that much difference in gas consumption between a 1/2 and 3/4.