Do NOT use royal purple as you do not want a fluid that contains friction modifiers. I'm not sure if amsoil contains this. This thread is a little over a year old and I can tell you that within the past year I've found the only other trans fluid to consider is the redline stuff. After using both redline and GM 88862472 several times, I'm confident saying that I think the RED GM gear oil(88862472) is the absolute best fluid for for the mu3 trans.

 

I second what XtremeSS said. I found a number of Cobalt SS websites with LONG discussions regarding what to and what NOT to use and they coincide with this information. The friction modifier was a huge no-no. When it came down to it, those that tested it and looked at the differences in wear all agreed...the GM fluid seems to be the best.

I got mine here:

Chevrolet Performance 88862472 - Free Shipping on Orders Over $99 at Summit Racing

 

Not that it matters, but the red GM gear oil has a unique smell to it as well. Rather pleasant actually compared to other similar fluids.