Best magnum MPG?

68 Fury four door, 5.2 magnum, 727, obd1 injection, 2.76 gears, it would consistently get 16 to 18 in mixed driving, 21 on a trip. I took the 2.76s out and replaced them with 2.94s and my best is around 20. The 2.76s are now in my dart, because a guy I know told me to :)