when accelerating bucks until around 50mph then stops if still doing it its very mild

my saturn sl1 has started a bucking action when accelerating. it started it out of know where 2 days ago, until then know problems. it does not miss and seems to be shifting fine. it does have the service engin light on and has been on for over a year and ran without an issue. computer check at autozone just said bad o2 sensor when they checked it then. weve looked at different sites they say bad egr sensor but that wasnt it. any ideas what it could be?