2002 Cavalier auto tranny problems

My cavalier has the 2.0L 60K miles and was running fine until a couple of days ago. It shifts really hard into 2nd and 3rd gear and occasionally jumps back to a lower gear reving really high and other times it runs relatively O.K. for a while.
I'm hoping it might be a sensor or somthing not the tranny itself.

Has this happened to anyone?
Would really appreciate any help
Thanks

There's no such thing as a 2002 with a 2.0L

2.0 is typo its a 2.4 got it mixed up with my NX2000