I've got an '00 with a strange problem. At a steady speed anywhere between 40-50 MPH (about 1600/1800 RPM)the LeSabre will feel like it's got a miss, or it's trying to shift out of overdrive lockup. It will "buck" two or three times until I either speed up, of take my foot off the gas pedal. This happens about twice a day. The check engine light hasn't come on, so could this be a transmission issue? There's only 59,000 miles on it. I would appreciate any ideas and suggestions.