I've had my XD since September and have always got decent mileage out of it. Usually about 20-21 on the hwy and up till about 2 weeks ago was averaging 18.3 overall. I've read that most people seen an increase in mileage at either the 6000 mile or around 10000 mile mark. I have just hit 12500 and its like you flipped a switch. I have set a new high 3 times in the last 2 weeks and my overall average has went up to 20.2. What really shocked me was that when towing my lawn mower and trailer this week I got 20.4 and in previous tows with the same trailer i had never got more than 16. Maybe my truck is just late to the party but I will take it!