Your mechanic actually does not know much about lubricants. They know that selling Amsoil does not work for them. They have people coming in 3-5 times a year for an oil change now they come in once a year. Not good for business. It goes deeper than that.
Use Signature Series ATF.
If you do not use Amsoil you will lose money from worse fuel economy, wear on transmission parts and earlier repairs.
Your mechanic makes big money if you need a re-built transmission.
Think about it.
( Amsoil makes many different transmission fluids to suit every OEM requirement. Just enter Make, Model, Year on the first page of the Amsoil website and you’ll see what goes in yours).