A few more details on my progress. I took the car to a couple of other shops, and they were both pretty sure the trans was not rebuilt and only the broken piston was replaced. Should have been around $400 total using all new parts and including labor. However, the shudder remains between 3rd and 4th. Any thoughts, anyone? Does this transmission still need a rebuild?

Also, I just noticed on my invoice that they replaced my broken piston with a used part. Do I need to worry about the longevity of this used piston? Does it make any sense to replace a broken piston with a used one?