Ok I install a GV overdrive in my 69 mustang about a year ago. 445 stroker, 850 holley,294s cam,389 gear, big in and out wide ratio trans 4 speed, 28 inch. tire. After adjusting carb. to what I like and MSD dist. I finally got to take the car on a 250 mile ride today. 85 % freeway at 75 mph at about 2750 rpm. Car ran great and I checked the gas mileage and I got 14.1 mile to gallon. I think that is great and I am very happy with this combo. Before todays ride all the miles were around town and never had a chance to take it on a long ride. Mostly been raining here in WI.Though I would share this and a big thanks to Jay, Ross, 66 Fairlane, Barry and every one else on helping with the carb,dist,and GV.