Last summer I had the same problem in my 76 Dodge Aspen with a slant 6 .I went thru the entire car prepping for a 2000 mile road trip.Put in a new fuel pump too.Went on the trip.Everything was fine but the morning after I returned it started to act just like your car is. I checked everything and finally came to the conclusion that the ethanol in the gas wiped out the fuel pump diaphragm . Bought another "new " fuel pump and the problem was solved.Don't assume just because it's new it's good