I heard the rumors going around when I first got my truck that they had a break-in period at 3500 miles. People reported better performance and mpg after that mark. Well I never really noticed a difference. My truck just recently rolled over the 7500 mark and it not only feels like there is more power all of a sudden, but I've been getting consistently 3-4 mpg better. Nothing about the way I drive has changed, although the temp outside is been between 5-10 degrees cooler. Anyone else experience this? Maybe its the cooler weather, but it sure is a nice change.