1999 Other Chevrolet Models 1999 Chevy Venture won't start

1999 Other Chevrolet Models 6 cyl Automatic 135000 miles

I have a 1999 Chevy Venture. We were at the gas station filling up when I got back in the van and it wouldn't start. We ended up having to be towed home. A mechanic friend of mine checked the fuel relay and replaced it, it started right up. He did say that the pressure was low and we would soon need a fuel pump. The following week, stopped running again, tried another relay, didn't work, so we had the fuel pump replaced. Again it started up again. Then a few days later, my wife was out running errands during the day, that evening we got in it to leave and it wouldn't start again. The next day we left for a long weekend(not in the van). When we came home we tried starting the van and it started! What the heck is going on. It is getting very irritating? I just don't want to get stranded anywhere! Thanks! I just checked the pass lock key and that's not it.