I would suggest a tranny flush at 60K miles if you drive it hard or use the "Steptronic" shifting like I always did. My tranny fluid was turning pretty brown at the end and I was right at 60K miles.
The AT on the Solara is really crap - especially the '06+!! You'll see more of my rants about it in here so I wont' go into it in this thread.
THe transaxle, however, should be an issue unless - as others have stated, you have a problem.
The tranny flush should help smooth out the shifting a little though.
Good luck!
Jeff