1989 Buick Park Avenue 89 park avenue dying and hard starti

I started having problem where 89 park avenue would die after driving about sixty miles. Could restart immediately and drive between 4 to 10 miles and then it would die again, restart and repeat the 4 to 10 mile cycle. Then it started also having hard starts with some backfire...then it would not start at all. It sat about a week and came back out and it started perfectly. Now starting perfectly. Have not tried long drive yet until get fixed, it is stalling sometimes on stops after accelerated speed. Any thoughts?