The common debate i know... but i have a '03 hemi all decked out with all the bells and whistles, but getting tired of it and want a newer truck. I wanna switch to a cummins but dont really need it. What are ppl getting for mileage with say '06 or '07 5.9vs 6.7 and what upgrades have helped the most?

 

on average most will see 15-20 on the 5.9 and 12-17 on the 6.7, the 6.7 cand be dramatically increased by disabling/removing the emmisions crap, but there are laws in some places, the 5.9 is strong and solid as is and there a lot of options for mods....

as far as gas or diesel, diesel has way more power, milage (in most cases) and a lot bigger price, but the initial investment pays for itself in in all thoes things, as wall as the longevity of the cummins

 

My 5.9 gets 11mph hauling a 29 ft camper and 14,15 empty. The computer is always shows higher. I don't know of one that is accurate.