2002 Lincoln LS hard to start when warm

I got this car 7-08 it runs great, no check engine lights or anything, the day after I got it I took the family for a drive no issues at all. What I noticed the next day the car was hard to start after coming out of the store I was in there for about a hour. If it does sit no longer rhan 30 mins. Its fine.I went to my local ford dealer they said it had the org. Fuel filter on it so they replaced that. It did not help then they said that the fuel soxs in the tank which probally weakend the fuel pump, that did not help, they said on the02 they were a tsb to reflash the pcm and the iac motor had to be replaced too. I left the car to have this done they said they would check it on the machine and to fuel pesure test too.I new from what I read I should have the valve covers replaced that was aweak point on this car while it was there. They also put a fuel rail preure sensor on it too.I got the car back after 1500-00 bill it does run better than I thought, but I still have a problem starting it after it sits over 30 mins. They say fuel presures are ok and they say they cannot find nothing wrong I do love the car but I know I am not nutts something not right any in-put would be great on what you think might be wrong I should have put the 1500.00 in the sherder at work I would almost have the same result. Thank you for your time