Slant Six mpg's?

..........My 67 dart gt made 16-17.....hwy........11-12 in town......pretty tired though........my 76 dart sport.....25 hwy...18-19 town.....my 68 dart 270 dont know as i only drove it 24 miles home.....changed to 340, 727 8.75 with 3.23s......kim.........