My first X350, a 2003, bought in 2010, had to have a "reflash" of the TCM to cure shift anomalies, incl rough and harsh shifts. That was all that was done and the car was then with me for over 100k miles, when I bought another one, a 2007 Sovereign. The transmission gave no more trouble, and neither did the one on my second X350.

 

did it take a while for the shifting to get better after the reflash

 

yes some will take a very long time or never adapt properly

all depends on how worn out the transmission is. some are smoked in 50k others make it to 500