I have a 06 3500 6.6 duramax with 17,000 miles. At 15,000 the dealer replaced the turbo. Since it gets 11 mpg. It got 19 to 20 before, unloaded. We have taken it back to the dealer and they say nothing is wrong with it. Does anyone have any suggestions on what to look for? I think there in a problem in the program. But I know nothing about how to check any of it. Anyone with an idea let me know.