1990 GMC S-15 intermittent starting problems

1990 GMC S-15 mileage: 187,000. I'm having a starting problem with my pickup, it is an intermittent problem. The engine cranks with plenty of power all the time. When the truck acts up a tiny squirt of starting fluid into the intake (with air cleaner cover removed and then tightened back to normal before cranking) the engine fires right up every time without hesitation. When the truck is running it responds directly to the throttle and exhibits no signs of sputtering or stalling. The problem most often occurs after a short drive allowing the engine to get warm and after the truck sits about half an hour it won't start. It seems not to be receiving fuel. Last spring I replaced the fuel filter and fuel pump. I live in the Northeast and I am wondering if the thermal changes point to the problem. Any ideas would be much appreciated.