I had a '69 Dart Swinger 340 with 3.23 gears that would cruse at 2700 rpm's at 65 mph with stock tires. I went to 3.91 gears and the rpm's went to 3200. I took many 400 mile trips from the bay area to LA with no problems. Mileage was not great, but high test gas was only $.25 a gallon back then.

Raul