1999 Taurus - Stalls in the summer!

My 1999 Ford Taurus only has 56,000 miles on it. When the weather is warmer (above 65-70, but usually in the 80’s or 90’s) it will die when I am slowing down. I never know when it’s going to happen. It usually starts after anywhere from 5-30 minutes, like it never had a problem. It now seems to be getting worse. I was stuck on the freeway for 45 minutes today and had to get it towed. It is also a little shaky when I am stopped, waiting at a light. My mechanic (and the computer diagnostic) can’t find a thing wrong with it. Any ideas? One possibility I found is that it might be the fuel pump. It absolutely never happens in the winter or early spring and the only lights that come on are the battery and oil. It has enough oil and it will still die when the gas tank is full. Help!