RKHiPerformance

I'm about to install a Pro 5.0 shifter in my Dad's '02 SS and will change the transmission fluid while I'm at it.
The owner's manual calls for four quarts of Dexron III, but is the GM Synchromesh fluid a better choice? What is the best fluid to put in there?
I did a search and found many conflicting opinions.

Thanks very much,
Rick

U240

I went with Mobil 1 synthetic ,it seemed to shift a little better and you supposedly pick up a few h.p anyway its been in there for about 30k with no problems