Do you know what your transmission temperatures are? What type of cooling setup do you have for your transmission? Once again I'm no expert, just throwing out ideas.
EDIT - Also this is unrelated but did you have BBP remove any torque management from the tune? If so I would have them put it back in unless you're OK with grenading your 4L60E in the near future.
EDIT - Also this is unrelated but did you have BBP remove any torque management from the tune? If so I would have them put it back in unless you're OK with grenading your 4L60E in the near future.