Thanks. I've considered carrying a spare gallon. My dash display was showing 0 miles to empty for the last 10 miles on the tank. That can be a bit unnerving.
I have a friend who bought a 2.3 liter Focus about 6 months before I bought my Mustang. He told me that he can get 29 MPG out of it if he's nice to it.
I must be doing something wrong.