MPG Increace

I had a 360 with 2.02 J heads, bored .030 over, .284 duration cam, 3.91 gears (28 inch tall tire) with a 904 auto. Carb was a 750 Holley dp. I got 16 mpg at 55 mph. It was in a 74 Dart Sport. The car got into the 12.90's at 104. I think you are down from where you could be.
Here is my suggestions. First, pull a spark plug. Should be cardboard brown. If it is black, then you are too rich and going down on your primary jets instantly helps gas mileage. You may end up going down, per say, from 73 to 70 jets on the primary and may instantly get 2-3 mpg. My 2nd suggestion is be sure your timing is set right. The best measuring stick for this is a drag way E.T slip. My 360 ran the best at 38 degrees BTC. Ironically, this gave it the best gas mileage too. 3rd suggestion is watch your driving habbits. Is it fun to feel a little "G" force taking off??? You WILL pay heavily for that. Drive it like a State Trooper is following you everywhere and he is having a bad day and he is annoyed at your car.... ! 4th suggestion is if your running 20w-50 oil, go to 10w-30. Less drag for the whole system. Good luck!