Hi I'm new to this website, I have a 2006 5.9 with 5inch strait pipe, air intake, boost fooler and bully dog td truck has great power and no other problems at all except terrible gas mileage consistently see between 8-10 regardless of tune or driving type, have read about dodge reflashing with new soft wear can help is this true?

 

That's really bad! How's the right foot control? A bad hole will do that! these engines are great at hiding a dead cylinder! Have a dealer do a cylinder contribution test!

 

I Drive it real easy all the time! I figured if I had a bad cylinder Id have loss of power? It runs just as strong as it did brand new, also I had my injectors tested and they all came back fine, would they not find a dead cylinder at the same time?

 

Check for blow by! If they didn't do a cyl comparison test you wouldn't know it the computer will compensate for it bad mileage is the only hint something is wrong!
Other things that would cause that are transmission slipping plugged fuel filter, under inflated BIG TIRES!