I had the same problem with my 98 GS. It started after I changed the ATX oil and filter. A mechanic told me it was because I changed the oil while it was cold. Apparently you are supposed to warm the oil to operating temp before draining it. Of course, changing the oil only drains about 2 quarts from the trans (valve body and torque converter oil remains). I did another drain and fill while it was warm and that seemed to have solved my problem.