Turn off the traction control and you should be fine.
I had my new 08 GT at Nashville speedway and just about every new Mustang had the same problem. It was just not GT500s. It was GTs, Roush, and GT500s. We were told that if the traction control was turned off, it would not heat up as bad and the overflow would stop. Sure enough, it seemed to help. The track people were really concerned with us out there cause some cars were noted that the diff fluid splashing on the inside of the tires.
There was a guy there that had a Roush 427R and he said that he was putting the catch can on his and already had it on his race car Roush 427R. He said the can was the only thing you could really do to solve the problem.