Car Stalls after driving for a while?

I've had some problems where if I was driving and turned on my AC, the car would stall when I slowed down. Usually only turn on the AC when on the freeway, not around town. Today, I was driving around town for about 20 minutes and the car heated up, it started stalling every time I slowed down. I knew it was time for an oil change, so I got one and they also noticed it had been overdue for a fuel filter, which I got replaced. Something they had not mentioned before, since I always go to the same place. After they changed the oil, they tried to start it up, and made "grinding" sound, so they let it sit a few more minutes and then started it again and it was fine. When I left, I wanted to see if the fuel filter was the problem, so I drove around for about 20 minutes and started doing the same thing, stalling when I was slowing down or at a complete stop. If this is just maybe bad spark plugs or something, I could take care of this myself, but the ford dealer told me they should be fine until 100K miles. Any help would be greatly appreciated.