Car slowed down and would not go any faster?

Hello, while I was driving about 10 minutes the car at the same time the a/c started blowing warm air and the car slowed down and would not go any faster when I stepped on the gas, it felt like it was in 1st gear. I pulled over and turned the car off then 2 minutes later I turned it back on and the a/c started blowing cold air and the car was running normal. About a month ago the check engine light came on then went off a week later. I took it to ford after the problem I had on the road. They said there was nothing wrong. I told them about the check engine light coming on a month ago and they said nothing showed up on the codes and nothing was stored in the computer that I even had a problem. One of the salesman said it sounded like it went into limp mode. Why didn"t they find any problems? They charged $98.00 and did nothing. I'm afraid to drive it fearing it will happen again. What could be the problem? Please help, if a ford dealership could not find the problem what should I do? Thank you very much, barbara