I paid $17,000 for my 2006 Duramax crew cab long box in the top trim line, leather etc with 185K on it and feel like I got a good deal. I was going to buy a 7.3 Powerstroke but all that I found were way over priced for their year and mileage. I think the 5.9 Cummins is probably a bit better engine than the Duramax but the Allison transmission behind the Duramax engine is much heavier duty than the Dodge transmissions of the same vintage... IMHO. The back seat of my Chevy has considerably more room than the standard Dodge Crew Cab which meant a lot to me because I have kids. The Dodge MegaCab is a different story as far as backseat room though... if you want a short bed.
P.S. Texas seems to have the best prices on used trucks and they usually don't have salt damage. I spent 6 months searching before I found mine locally. I was just about to give up and take a road trip to Texas.