Just today i was wondering why I couldn't get quite up to my normal average on the last two tanks, then this post reminded me that I didn't check my tires after the last oil change I had about the time the mileage dropped. Got home tonight and yep, they had reset them to 32. So... while there are always many factors influencing FE, this reminder makes me likely to believe that the pressure does make a difference, expecially considering this is the second time it's happened this way. I will try to drive the same the next tank and see if it goes back up with the tires back at 40.