should be able to cruise way under 2500 rpm,,,some thing in his carb or timing is out of wack,,most cars with O,D cruise under 2200 rpm on the high way,,,until i do the O,D trany thing im going to a 3.91 gear,,with my tall tires,,i have 2 giant 4 bbl carbs,,and have tested cruising around 1600 rpm the car runs smooth and pulls it self out nicely,,with no bucking,