Since the problem seems to be more than just the coupling, I have a feeling the problem has something to do with the lift hill since they've been seen working on the top every night. Maybe its the anti-rollback system in place or something with the lift itself that needs to be changed/modified. But the biggest fix this coaster needs is in the computer program that it suppossed to allow 7 trains on at a time, which it is currently not.
Also another thing discussed it maybe with the new wheel on the trains, there is a smaller chance of another train valleying after the loop.