Nobody can seem to tell me what the problem is either. Have you any luck finding an answer?
I have a 2001 Chevy Impala but the miliage is higher than yours.
I have a 2001 Pontiac Grand Prix with ~43,000 miles. About 2 months ago the transmission completely imploded, and was rebuilt by a local garage. Since then the shifting has been a bit 'jerky' in the lower gears. Then yesterday the check engine light came on and the shifting got much worse.
I checked it out with a code reader I borrowed from a friend; it came up with Error P0742, which according to the book means the Torque Converter Circuit is stuck on. Not to sound dumb, but I know almost nothing about transmissions: Is this a transmission problem or something else? Would it be covered in the warranty I got from the garage who rebuilt it?