My buddies old ford had a similar problem. good battery, starter, alternator. but what it ended up being was the coil, all i did was loosen the screws on the coil and scuffed all the contact pints with sandpaper. when i reassembled it everything worked perfect. this was after he replaced a perfectly good battery and starter against my advice. anyway i would say to try the coil and see what happens, nothing to lose.
