I have a 97 Ram 2500 5.9, two days ago while doing some work for a friend I got into the truck and drove to the store about 5 min away, was only in the store 3 or 4 mins. and when I tried to start the truck it gave a puff of power like it was starting but didn't. I tried four or five times, then looked under the hood for anything obvious, didn’t see anything so i closed the hood and gave it one more try and it started and ran fine back to the friends.
After about two more hours of work when we got done we came out and the truck started right up with no signs of trouble on the 45 min. ride home. When i parked and shut it off the wife said that we needed to go to her sisters. After 40 mins. or so the motor again gave a puff of power like it was starting but didn't. So I called a mechanic friend of mine, who said to check the pick-up coil and the spark plug wires, but there was nothing wrong with them, lots of spark and it would still not start. After two hours from the time i shut it down the thing started right up so i began to think that it would only restart when it had cooled down so we drove to her sisters but after three hours of being there it would not start and after quite a few tries we finally gave up and got a ride home. went back the next day and tried it several more times but still nothing. Called a roll back to get it home and you can guess, when he got there the thing started right up.
it drove home fine running smooth, no hesitating and lots of power during the 1 hour ride home. Before turning it off I picked up the mechanic friend of mine so he could see how it ran before I parked it . sure enough when we parked it it wouldn’t restart after giving that little puff of power like it was starting. He swears he thinks it is the fuel pump but I read thru a few other posts here that are similar and there was mention of the temp coolant sensor and the IAC (Idle air control valve).
Any suggestions would be gratefully appreciated. I know this is long winded but at least you know the whole story other than 97 2500 Ram won’t Start when hot.

do you hear the fuel pump prime when you turn the key on? It does sound like fuel pump to me but I would double check for power at the pump to be sure before under taking the big job. You will want to rule out the fuel pump relay and auto shut down relay as well. Spraying some starter fluid in the throttle body or couple onces of gas and then turn it over , will confirm it is a fuel problem.

usually with the iac, if you hold the gas pedal down a little, it will start but only with your foot on the gas.

I hear the fuel pump cycle when i turn the key on.
i switched around the relays to see if they made a difference but to no avale. don't know where the fuel shutoff is or the relay. I wish i had a manual for it.
thanks for your ideas