Just turned 24000 miles. Use stations that sell alot of diesel except this past fill-up I decided to try bio-diesel and i'm pretty impressed. I think I will tow next time back in stock mode and see what that does. But I think this will give me a good excuse to buy a t6 chip. Since that seems to be a popular choice around here maybe you guys could tell me if you noticed any increase or decrease in fuel mileage while towing with this chip.