1997 Ford Crown Victoria engine question

I have a 1997 crown victoria. When i'm driving down the highway, I set the cruise control at 65-70 mph. It drives fine for about 10-15 minutes and then it looses power and drops down to about 45 mph. When it does this I tried to push on the gas and nothing happens, the engine doesn't rev up or anything. So I pull over to the side of the road and shut the car of, I wait for about 5 minutes and start the car back up and it does fine for another 5 minutes. It doesn't just happen with cruise on thats just when it happens the most. I was told that it could be the cadilatic converter, but wouldn't it happen all the time if that was it? I'm kind of at a stand still, so if you have any suggestions please let me know. Thanks