most if not all race tunes keep the converter locked under shifts, but it doesnt really matter in 4low because the torque has been taken off of the trans, so actually the transmission should be fine.
here is a truck with a lock up switch
http://youtu.be/kC6blhcnZXE
here is a truck with a lock up switch
http://youtu.be/kC6blhcnZXE