Ya it was shocking to me also. I was talking to my amsoil dealer about my tranny problems. Told him about the grinding and its not wanting shift smoothly.
So he told me that he runs 20w50 in his tranny(toyota paseo manual) and has had no problems. I was so sick of the grinding that I just did it, and it is just wonderful. It took about a week for the new fluid to disperse the older thicker stuff but during that time it kept getting better and then after a week it was great.
I would definately suggest trying it, and if you don't have the same results within a week I would be very suprised. I think the stock fluid is just too thick. I don't think it allows the blocking rings to engage properly and that's what is causing the grinding.
I have over 10k miles on my car with this fluid and it is fine. Over 92k miles on the car all together.