I had a problem like that once with a 1972 Pinto. I could drive 16 miles to work with no problem. If I went on a long drive on the interstate sometimes it would start losing power and almost die. About the time I got to a stop it would pick back up. I checked fuel pump for pressure and volume, all OK. Drove me nuts for about three months until on the way home from work it died and wouldn't restart. No gas from the fuel pump. I put a pump on it and never had the trouble again.