2.76 vs 2.94 gearing

You said freway driving, that means 2.76. My 67 Dart 273 2bbl 2.71 gears, 225-70-15 rear tires. Get 20-21 mpg. A big help would be the A&A Transmission part throttle kickdown kit, it helps drivability a bunch.
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It's free to manually downshift at any time you feel it's needed.