I just bought my first duramax its a 2006 LLY 3500 4x4 dually. It had 228,000 on it when I bought it. It seems to run great and mileage around town is 15mpg. But labor day weekend we took on a road trip about 1000 miles total. It got almost 20 mpg I never got that out my gas motor. My question is how can I tell if any modifactions have been done to drivetrain. The guy I got it from was the 2nd owner he had the turbo replaced at 215000. But he said nothing else had been done by him.