That seems a bit low to me, even for a dually. Do you have a boost gauge or or a pyro? Are you getting any smoke out the tailpipe? It would seem to me that if you were getting that bad of fuel mileage you would be making smoke of some form. That would be indicative of maybe a boost leak. Do you have a plastic end cap intercooler? Those can fail even under stock conditions. If you have low boost, or high egt's for one reason or another I would say you have a boost/fueling issue.
That's what I've been thinking and reading. This truck should be getting better economy out of it than that. No gauges in the truck. I've thought about adding them, but don't the slightest clue how to install them (not the guages, but the sensors to send the signal to the gauges). Plus I figured with a stock truck I shouldnt really have a problem as long as I'm not over-working the truck.
The intercooler is the stock one with the plastic end caps. Looking at it, I didnt see anything obvious with it. (cracks, coolant leaks, etc). Any thoughts or ideas?
As far as smoke goes, there isnt any smoke with it when it's started or running. The underside of the daully fender/bed is not stained black. I do however get some smoke that I can see in the mirrors if I put the pedal to the floor from a dead stop or in motion. I mean I'm not flooding out intersections but you can definetly see some especially at night with the headlights of cars behind me. It's kinda a Blackish Gray haze. Transparent but definetly a haze. Nothing really noticable during light to normal acceleration. This normal or what should I start checking?
Thanks for all your help so far.