2004 Prius with odd surge at stop



My Prius has 80000 miles and has been a jewel. But 2 wks ago on a 1000 mile trip it began acting-occasionally-oddly. By that I mean either the brakes began to slip just as it was coming to a stop (less than 10 mph) or the engine actually accelerated. It did not happen every time I stopped and the effect, though startling, was subtle enough that neither my wife nor I could be sure which of these things was happening. My wife had it happen when she was driving and it is her opinion it was the brakes. Nonetheless she also had a time when the car was running but in park when it seemed actually to try to jump forward for no reason (she was in the passenger seat while I went in to get something so there was no contact with any of the controls). I am not at all sure what the problem is. At any rate we took it to a dealer (2 actually). The 1st said, based on our description, he was sure it could not be the engine or transmission, was skeptical about the brakes, did not know what it could be. They, however, did not have time to check it out. So we waited a week to get to another dealer a little closer (still 80 miles away) during which time the problem seemed to subside. So when we did take it in, they could not get it to happen, had no idea what the problem might be (have been). Anyone else have any experience like this with a Prius? We are stumped.

Thanks for your thoughts.