When I first start the truck, everything is fine, but let's say I drive for an hour and stop at the store. When I try to start it again to leave, it takes two or three tries to do it. I've already changed the spark plugs, the distributor cap, and given the truck a tune-up. Anyone know what may be the problem?

 

sounds like the fuel pump is overheating. does it make a difference if the tank is empty or full? Do you have a habit of running low on fuel? The gas actually keeps the pump cooler.

 

Get a Haynes manual and a cheap multimeter. Sounds like you might have a bad engine coolant temp sensor or even a bad IAC. With the meter and manual, you can test most of the sensors.