1997 GMC Safari fuel

Engine Performance problem
1997 GMC Safari 6 cyl Automatic

ok now my gmc safari was having trouble starting up every morning, then finaly when it would start up it was good all day. But recently it just didn't want to start any more and it left me stranded. Well my brother in law worked on it for me and he said it had something to do with my fuel pump, well he replaced the fuel filter, and it still did the same problem only now it would start up after a while but when he would push on the gas pedal it would shut off so he replaced the pressure regulator, and also the fuel pump, Then finally it started up and even when he pushed down on the gas pedal it wouldnt die. So I came home called it a day. In the morning when I got up to go to work I started my gmc and it started up fine with one shot perfect. When I was at work and I was leaving for lunch the same problem happened again it didnt want to start up any more so now what can the problem be?