Got a 07 6spd man 2wd dually with 17k miles. Drove it roughly 700mi on freeway @ 75mph and lie-o-meter says 17mpg. The mileage sems to go UP as speed increases from 65-75mph. Seems a little wierd to me. The rpm at 75mph was about 2200rpm. (from what I have read, I would expect the mileage to decrease as rpms rise) I was considering putting in the 342 gears as I only haul/tow heavy a few times a year to increase my everyday mileage.

Any thoughts or ideas? (vehicle is completely stock)

Also, while using cruise-control when you hit the increase speed button there is a 2-3 second lag before the mileage/power surge. Is that normal? My 06 5.9 would immediately respond and kick up the speed. (6spd man, as well) The other issue I noticed is that when you get on the gas the acceleration is not linear like the 5.9. It seems to take a second or two before the truck responds. (is all this normal with the 6.7 engines)

I also got my first check engine light half-way home!! ;o) Thanks in advance for any ideas/advice, Scott

 

Bump for ideas, Scott

 

go back to the dealer and have them look at it. it only had 17 miles on it when you got it...did you test drive it and did every thing work fine then?

 

Stopped at the dealer today, they were too backed-up to look at the codes. Told me if it wasn't flashing bring it in next week. Anyone else? Scott

 

Possibly it was needing a regen and was shut off before it could ever complete a full one. Previous owner might have been using it as a grocery getter. Then as you were hammering it down the highway, probably driving it harder than the previous owner, it was clearing out the soot. I know mine will regen for at least 30 to 45 minutes @ 75 m.p.h. The lie-o-meter will drop to about 2-3 m.p.g. AVG. lower when in regen and then the lie-o-meter will start creeping back up as it completes it's cycle, all while on a steady cruise controlled 75 m.p.h. My r.p.m.'s @ 75 m.p.h. with the auto/4:10's are right at 2k.

 

I figured the mileage will go higher with the different gears(342s). So, I will go ahead and order them. Sounds like the auto tranny is still geared different than the final drive on the manual. Do you have any ideas on the cruise control issues? Thanks again, Scott