About a month ago my car started overheating driving down the freeway. When I pulled over the temp came down and it does not overheat when it idels only when being driven over 80kmp. I also noticed that is is not shifiting into overdirve. I took it to a mechenic and he changed the transmission fluid and filter thinking that would solve the problem. It did not and now the car is acting like it is going to stall out when I am at a stop light. It feels like a little bump in the car and the RPM's dip just a little bit. Any idea what the problem could be?