BV,
Be careful on that one. As you read this mine is in the shop again. This all began in May when the dealer that used to work on my truck reflashed my PCM. Since then my mileage has gone straight down the commode. I used to get 14. 8 round trip towing a boat (app 4500# dry) from Denver over the continental divide to Lake Powell and back and about 16. 5 combo city and highway driving. Since the reflash (I would get the numbers but the rig is in the shop) I got around 12. 5 combo and towing to Lake Murray in Oklahoma I got an unbelieveable 9. 4 round trip. To say I am concerned or worse is very accurate.
Now what the dealer is doing today is an oil change and check of the IAT, PCM and anything else a good diesel mechanic can figure out. I say good because this guy took the time after the old dealer and their mechanic told me "there is nothing wrong with your truck and it's too bad about your mileage but there is nothing more we can do". Anyway this guy took the time and found a pin hole leak in my waste gate, since then the mileage has gone up by about 3, but no where close to what it used to be. So he is going to try again. I told them I would pay for a reflash of the PCM if needed but the mileage is about what I would expect from a V10.
I will repost with the results after I get to check it out.
By the way I am going to have a Bill K recommended mechanic redo my trans in about a month.
Good luck.
Dave