It is rarely ever the transmission brainbox. First thing I would do is
change the filter and fluid and see what happens when you do so. Alot of
time on newer car, this is all you need. There is no such thing is lifetime
fluid... those who believes that will need transmission overhaul anytime
after 100,000 miles.
On modern electronic transmission, it can be individual electronic part that
go bad and dealer will just change that only part. Do you have any 'Check