On the vehicles I care about I use Amsoil synthetic ATF. I have used it for over 10 years and have always been happy with performance. One thing I like about the Amsoil brand is it can be mixed with any other kind of ATF without any ill effects. This is important because there's always going to be about 3 quarts or more of old fluid trapped in the torque converter. I have never tried Royal purple brand, but suspect it's of the highest quality. As long as it meets or exceeds OEM specs for Dexron II (what Toyota originally intended here) & as long as it can be mixed with standard Dexron II/III it should be fine.

If however your problem started with the introduction of the Royal Purple, then it's too big of a coincidence & I would want it out of there. Tim