Transmission was setup by putting the final gear ratio almost all the way up, then moving the auto setting all the way wide and then back down to sports (24). Then moving the final back down to 3.166. Adjust final gear ratio and individual gears for each track. If you move the auto setting it will reset the gear ratios.
Tokyo 246, 15 lap professional race in GT All Stars. Changed tires every 5 laps (at end of 5th and 10th laps). Finished 1 minute 14 sec ahead of 2nd place and lapped everyone else.
The setup above is more of a drifting setup that worked pretty good for a lot of tracks. Some tracks it's not that good for such as Seattle Circuit. I found Seattle Circuit much easier to keep all those settings, but change the LSD Init. Torque to 18 and the LSD Acceleration to 40.