I have a 2007 Highlander Hybrid with 96,000 miles and just changed out my transmission and read differential fluid (I doubt it had ever been done before). A couple of notes from my experience:
I bought the car used, but my sales sheet said the vehicle had the tow package. The dealership told me that the trans would take 4.2 quarts with no tow package and 4.4 quarts with the tow package. When I drained it, I actually had about 4 quarts come out and that is about how much I put back in. Also, when I opened the fill plug, fluid did start coming out. So it was filled some amount higher than what I could put back into it (I did have it on a level surface). The transmission fluid was a light brown color and no longer red. Unfortunately there is no magnet on the drain plug. I plan to re-check in a couple of days to make sure the level is still good.
When I drained the rear differential the fluid practically looked like it was new. The plug is magnetic and it did have some very fine black material on it that I wiped off. The fluid looked so good, I don't think I will be doing this again for a very long time. One thing to note is that the rear differential hex plug did not take the 10mm hex socket, it was slightly smaller. I believe I ended up using a 3/8 hex socket instead and that fit pretty snuggly