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.