The reasons newer diesels have horrible millage is because of the epa crapola. If there was no emissions control on diesels I BET todays diesels could get 30mpg because the engineers could focus on economy, durability, and power instead of worrying about meeting emissions standards. I dont believe in more hp = less mpg. Why does a stock 12v have say 200hp and 450 torque and get 20+mpg?
I drive a diesel because I like and know how to work on them. Yes millage is better, but parts, fuel, oil changes, etc are much much more than gas vehicles. I can't stand people who own diesels and pretend that they know everything about them...