stumbling pontiac

my 1996 pontiac grand am stumbles once in a while ... happens most of the time in overdrive at around 55 miles an hour. have noticed it to do it once in a while at a lower speed in third gear. i have replaced trans filter, gas filter, seems to be better since changing the trans filter out. had a scan done by a pontiac dealership they come up with nothin wrong. does any one have any info?

what motor?

what motor?
2.4 L also is an automatic

This can be an ignition problem, only happens under load, possible coil, or plugs.

yes, this sounds ignition related. Try replacing the coil housing cover, they are about $40 at a parts store.

thanks, i will look into that