Check your tire pressure. For the the first 100 miles or so after I left the dealer my mileage was about 12 mpg. Then I checked the tire pressure. It was up to 20 psi low on some tires. After I filled them to proper specs I am getting about 15-16 mpg empty and 11.5 towing 4k.

 

Calling dealer tomorrow to make appointment to check it out, we'll see if their is anything wrong or if that's just where these trucks start out on mileage. I have been running PS additive about every other tank unless it is really cold when i fill up then i always put it in. Just kind of disappointed so far as that was one of my main reasons i bought the truck was because everybody always raved about getting 20 mpg. Hopefully it gets better and their is nothing wrong with the truck, so far i love it other than the mileage.

 

I tried checking for codes as well, and didn't get anything to happen, only showed the odometer reading, maybe i don't know how to do it. Just turned the ignition off and on 3 times, and didn't do anything??

 

I live in canada and bought an 06 cummins 4x4 quad cab. I have had nothing but problems and the truck has had 8 injetors so far . Taking it back for 2 more this morning . They blame it on fuel . As for the vibration on the highway , mine did that and we found the wire connector on the fuel pump actuator was not making contact all the time.This will make it vibe and smoke .