1974 valiant stalls in gear 225 automatic

1974 valiant 225 stock carb . automatic . when i got back from going to carlisle from new jersey a good 3 hrs both ways no trouble at all until when dropping off a friend almost all the way back . i filled the tank at a gas station i never used , probably at least 3 quarters of a tank . ( maybe its the gas ? ) then , when starting right there , and put in gear , the car stalled , cut right out . so now and since then , if you put it in drive or reverse , it either dies or barely runs with a very low idle . fast idle is high curb idle is around 800 rpm ( though i tried upping the curb idle to 1200 ) , still falls flat on its face when put into gear . unless i also hit the gas at the same time . then it will go and stay running until i get to a light . occasionally it stays running , again at very low idle , almost cutting out , but usually dies . any opinions or suggestions . is it bad gas ? should i mess with the idle mixture screw ? or am i missing something entirely ?