I have a 2006 Toyota Tundra w/12000+ miles. I recently took a trip in the mountains and noticed, after driving for a long period that the tranny "hang" shifted, especially going down hill. Has anyone else had that problem? I would have to kick it into netural then back to drive to get it to shift.

You should change the fluid every 15,000 miles. I would switch to a synthetic like Amsoil. Im a dealer so i may be biased but i've used it and have never had complaints only good feedback. Toyotas do awesome on Amsoil from my experience. Good luck.