ETS off / check engine Problem.

ok, i baught a used 1999 chevy cavlier about 5 months ago... i noticed one day that one of my warning lights came on ( ETS OFF) when this light came o my engine seemed to shift harder... now it comes on more frequently and when it does my car shifts Very hard, and the only way to correct it that i have found is by putting the car in park, shuting it off and restarting it and putting it in drive again... that usually give me about 5 mins before this problem occures again. its really annoying and i need a car that will work. i brought the car to an mechanic and they drove it around for a while and noticed nothing.... Pleas can anyone help me?
i just wanna know where to start.
-thank you sooooo much for your time!
-mike

go smack your mechanic. Get it on a computer and see what that code is, autozone will do it for free. My be a tranny sensor