I would thoroughly clean and verify all of the pins in the mechetronic plug. If it is truly rebuilt correctly than my money is on a bad connection at that plug (back side of the transmission), either contamination, bent pin, plug not seated all the way and the collar locked, leaking sleeve, etc, etc causing the signal from the trans to the dme to get "confused".


EDIT: It is possible that they did not get the linkage seated correctly when they reassembled the transmission, but if you have been able to drive it for any distance, that is unlikely.. and it most likely wouldn't have anything to do with it jumping in to Sport mode - though that plug may.