Looks like the issue was a shudder on light acceleration between 20 - 40 mph.
In one case they replaced the entire transmission, and the other just the torque converter.
It would seem the torque converter was the cause in both cases.

Having said that I don't believe anyone with an IS has reported this issue so far...which is good.

 

When I bought my IS350, I got the V6 AWD because both the engine and tranny have been on the market for a long time in many vehicles and all of the bugs have been worked out by Toyota and Lexus. Honestly I just wanted a nice, fast, reliable car. That is the IS... just go drive the thing HARD and change the oil and it lasts for ever.