I saw mine around 3500 miles as well - most of tanks up to that point was around 42. When I was around 3500 I got around 45 for a couple of tanks. Now I'm around 53. Still driving the same - I tried going no AC (windows and fan) but did not see any noticeable affect on my mileage for the last 2 tanks. I'll try 2 (I go through a tank every 4 days - about 600-650 miles/tank) more before I go back to Auto (usually set at 69 or 70).