Well, I just had my transmission rebuilt in my 1997 Chevy Silverado. My Chevy had 250,000 + miles before it went out. We used to do work at the shop I work at, for a guy who ownes the tranission shop I had mine rebuilt at. His words about changing fluid or flushing a transmission was this. He said that new transmission fluid had a lot of cleaners in it, and that will wash away any build up of material that will have deposited on the bans and clutches. So in doing a fluid change or flush a lot of the time, it makes a transmission slip that was not slipping before. Chances are, if the fluid is turning brownish, the transmission is already waring out. As the owner of the transmission shop told me, run it until it quits, then have it rebuilt. When my transmission went out, I was still able to drive it. It just didnt have R or OD. I drove it to his shop. 1 week later,my truck was fixed. Cost me $2800. It may be more for a Toyota, IDK. Maybe make some phone calls to a few local transmission repair shops. It is not necessary to have you local Toyota dealer to do this type of work. A trick to finding a good shop is that a good shop will be busy.