The newer the year model, the more emissions crap and the worse the mpg .
x2
My 2000 7.3 powerstroke has 252,000 miles. I have a superchip that leave on the 90hp setting. I have a straight pipe(no muffler) and a high flow air filter. I drive it everyday and get right at 20mph on the highway unloaded. I wish they made them like they used to. My power windows roll down kinda slow, my drivers side front seat is worn out, and I've had to replace one injector and one front wheel hub bearing.
Circle C is right on about the '03-'04.5 Dodge. Any of the 7.3L powerstrokes should be good too. I think they are '96-'01
My dad's '08 Duramax gets like 12 mph unloaded on the HW. It sure is a nice ride, but they don't seem to make them like they used to.
