Ok Last year I had some problems with my 72 440 duster, going and coming back from a show 3 hours away, the car starting bucking and surging on our main HWY, speed was between 65-75 MPH. Even quit and would start after awhile and even right away. got it home. replaced my Fuel Regulator with a Mallory with return line, changed the vent line. Thought this fixed it but had not had the car on the main HWY since then. Been to the track a few times and all was ok. Made a trip Friday night but took a secondary HWY and speeds were only 50MPH, no problems going there, 50miles one way. Coming home decided to take Main HWY Speeds were the same as the first time it started acting up, and after 20 minutes it started to act up again so got off main HWY to drive on secondary one, all was fine for 10 minutes or so then slowly got worst to the point of having it stall which I finally pulled off into a parking lot. Started right up, Idles fine, left again and got some Ice to put in cool can but did make a difference, barely made it home, Ok what's could this be?