Like Sid said, emissions control is cracking down on diesels. Personally I think its a waste of time (a diesel rolling black smoke is more "green" than any gasoline engine. the black is soot and its not toxic) I like diesels more because of the "work power" and longevity. With moderate care to your engine, it will last longer than the body and frame.
The newer diesels (specifically Cummins, and after 2011 I think), they started pushing "cleaner/energy efficant" diesels. Meaning they made it mandatory that a LOT more computers/"emission" controls where installed. Up until like 1993, the Cummins in the Dodge trucks where all mechanically operated. Then came the second gen which had basic wireing and computers (for like ABS and auto transmissions ans such). The engine was generally left alone. But around 02-11 they started pushing more electronics in diesels (for dodges anyways).
Having a newer diesel is not the end of the world, they work just find and dandy. I would never own one because they one pain to modify (you trip one code and your screwed). But if you need one for work or play, they will preform and exceed your needs. The Cummins line of engines is one of my favorite and I'd say second to Cat engines, you cant go wrong with them.
BE WARNED, you are buying a Dodge. I'd rather pull my 20 foot dump trailer by hand use drive a Dodge (trans sucks, computer is the worst, a metal seat and two springs offer better suspension...). You have a decent chance of getting a better built one buying new/er, but just go into this eyes open. Dodge has the best pickup engine and it has the best axle (Dana 80 is the hands down best rear end for 1 ton and larger pickups).