Re: Need advice with possible transmission issue!
It certainly sounds like it could be the torque converter.
There is a long-standing debate as to whether it is worth just changing the torque converter without changing the transmission and vice-versa, because if one goes it is likely caused by the other and/or can contaminate the other with the debris from a failure. Many recommend replacing the torque converter and the transmission as a set. Many also say it is fine to just do one.
Since you are under warranty, you don't really have much of a choice in how they want to fix it, so it's a moot point.