[89lxinwky]

I had an '87 GT with 3.55's and basically everything else stock for 6 years. I drove from Kentucky to New York in one day and got well over 20mpg. I also had a 3 1/2hr drive home once or twice a month and got the same results when mostly highway driving. In my current car I have 3.73's, I don't drive it very much and usually it's stop and go and not much highway driving. I get about 14mpg but I can't compare the gears because I haven't made a long trip with the car yet. 3.55's did not hurt my gas mileage at all and they performed pretty good. I like the 3.73's better but I don't know what they will do to your mileage for highway driving. Maybe someone who does some highway driving can tell you that.