T-45 or 3650

I am reading a book written by Sean Hyland. The transmission chapter mentions that Ford switch to the 3650 in mid-2000 and by 2001 all were 3650's. Does anybody know what production month in 2000 did they start using 3650's? Or how can I tell by looking at my 2000 GT? thanks
 
In order to identify what kind of Mustang transmission you have, you need to check the door tag on your drivers side door jam. If you look down to the bottom right of the tag, you should see an area labeled "TR." Underneath this label there are 5 letters and numbers. The only one that we are concerned with is the first alpha-numeric character which corresponds to your Mustang Transmission.

If you have a 6 as your first digit, you have five-speed manual, T-45 OD Mustang Transmission. This is the standard Mustang transmission that is found in 1996 to Mid 2001 Mustang GTs as well as 1996 to 1998 Mustang Cobras. If you have a 5 as your first digit, your car came with a T-5 OD Mustang transmission. Finally, if you have a K as the first digit in the "TR" code, you have a TR-3650. This Mustang Transmission is found in mid-2001 to 2004 Mustang GT, the 2003 and 2004 Mach1 and the 2001 Cobra. The 2005-2007 manual Mustang GT's also a T-3650.
 
GTs produced before Feb 2001 came with T-45s. Feb 2001 and later had TR-3650s. See the manufacturing plaque on your driver's side door to see when your car was built. Also, as mentioned above, you can tell by the transmission code on the plaque which transmission is in the car.