They are the same 2012 onwards for the LFX
2012 transmission to end of VF I believe are the same but I definitely know that 2012-2014 are identical it's just the TCM code that changed that is why you now have a 2012 transmission as I flashed your TCM with the 2012 code to match your ECU which also now has the correct 2012 code in it and they are happily talking to each other instead of like the last clown who work on it just turned off all the transmission error codes so it looked like they were happy! - Big Difference
There was thread on, l think tailshaft vibration, or something like that a few weeks ago. There was a tsb (gm service thing) can't remember exact details.
But bottom line was tailshaft was dropped to allow the back of trans to be able to come of, cleaned up & coated with lock tight & put back together. It was stop some sort of vibration?
I think
@lmoengnr added that there was tsb about it & the fix?
I tried to find the thread, but couldn't.