TD5 Auto Gearbox

I have just had a heavy duty torque converter fitted to my TD5 in the hope of getting rid of a vibration coming from the gearbox area at 2500 -3000 RPM. The vibration has gone but the car does not change gear smoothly. I am starting to think that the old torque converter was masking a worn gearbox. Can please advise if they have had similar issue with auto box. Thanks in advance.