I currently own a 07 dodge mega cab 6.7, nice truck but man does it love the diesel and im about to get rid of it. Im kinda new to the dodge cummins so don't know too much about them. I'm looking forward into buying a 5.9 (05-07) and just want to know more about them. I'm not much into the horsepower or towing ability. I'm just looking to have better fuel mileage on a 5.9. Would a chip or programmer help the fuel mileage? If so, how much better? And which chip and programmers would be the best?

 

I went from the 07.5 Mega 6.7 (I loved the HP, but like you it loved drinking that diesel) to what is in my sig. Totally stock except I no longer have the CAT cause it broke. I'm getting about 16mpg in the city compared to the 6.7 was getting maybe 8mpg in the city. I can't help in the chip / programmer dept. but I dream of getting a Smarty Jr. someday. You will love the 5.9 w/ no emissions to worry about like you do on the 6.7!!

 

I currwntly have a 05 5.9 wish i had the money for a 6.7 my old man has one and he walks past me in the mpg area as well as blows me away with hp and torque. My 5.9 is all stock except for a 4in tbe and im lucky to hit 16.5 mpg hwy where the 6.7 with the deletes, 4in tbe and a smarty jr will push 25 mph hwy...

 

I believe the mileage champs in the common rails were the 2003 and early 2004 motors. The 2004.5 and later 325hp motors all had catalytic converters and the cam was ground for emissions considerations having what they call "in cylinder EGR".

The "Smarty" downloader for the 2003 to early 2007 models does have the advanced timing tunes which will yield maybe 1 mpg or so. "EFI Live" which is only for the 2006 and 2007 5.9's I think can be easily tuned for mpg.
Don't know much about the other programmers, sorry.