I have a Mustang with a T56 installed. I assume it was used [when installed] so miles unknown. The issue is the second gear downshift at times. I don't recall the issue before the fluid was changed. The fluid was nasty looking. The trans said on it to use Dextron 3, so I did. I'll have to see if it is a synthetic blend, but either the transmission synchro is worn or it doesn't like the fluid in it. Anyone run into this or know the best fluid to use? First and second synchos have a friction material added to them.