problems when car changes gears

I have a 2000 Chevy Cavalier. It's an automatic. Sometimes when driving, when it changes gears, it jerks like its having a hard time switching gears. Sometimes the trac off light comes on, sometimes not. Can anyone help?

I had this problem before...when I put my new intake on I forgot to reconnect the Intake temperature sensor. It plugs into the intake. Or you could have a genuine tranny problem. After driving a while with it disconnected the check engine light will come on followed by the trac off light. Then the car will shift very hard...like you put a shift kit in it.