es202

i need some info from u peeps... when i'm driving my car say about 80km/h or less,shifting is really bad as if i'm using a manual gearbox.shifts badly that it had a "thumping" sound especially when downshift.. but if i drive her like say 160-200km/h.. no problem or what so ever on shifting.. it runs smooths!! no "thumping" sound.. feels back like driving an auto transmission...

what could it be? geabox problem?(Hopefully not)and if so.. is there a ATF Kit seeling around? or could it be Torque converter? or maybe the front & back coupling or simply just the ATF Fluids is low & dirty? i really need help on this guys