Intermitting problem on 1999 GMC Safari Van

Day before truck starts for a instant but stalls & will not run at all. Yesterday truck started with 1 try had no problem all day. This morning same as the day before with same type weather for all three days. I didn't have this problem until I replaced spark plug, wires, cap, button, air filter, fuel filter. Since the problem started I have replaced fuel filter( again ) & fuel pump. I have driven the truck over 700 hundred miles since problem started so its not the fuel. Truck runs great when it runs