I have been having the same problem with my 2004 Tiburon. My car is also around 50K. I recently got my transmission replaced under warranty but I am still having issues with the slipping/jerking feeling. I took my car back two times since and had the Manager road test my car with me. After the road test they took the car in and reset the adaptive values on the engine and the transmission, they also checked the fluid levels and disconnected the battery. After all of this my car is still acting up. I have left a message for the Manager and have yet to hear from him.
Have you had any luck with your car? Does anyone have any advice?