Just got my transmission rebuilt(4t60-e) and now when the converter locks up, the car starts to shudder and vibrate really bad. Any ideas?

Is the torque converter new? It could be something unrelated too. A bad miss, some sort of EGR problem or catalytic problem could make it jerk and buck too. It seems like it would throw a code if it was a TCC problem. Good luck, let us know if you figure it out.

I agree. Once the converter locks up there is no "cushion" between the engine and trans. So, a miss will be felt more easily. A torque converter malfunction will set a fault code.

Does the shudder only occur momentarily while the converter is locking up or does it occur all the time while the converter is locked up?

All the time, probably a bad engine miss like above

Thanks