Originally Posted by Ryan @ RJM

Meulen,
I don't sell the Redline or Amsoil products but you can pick them up locally thru any speed shop that carries them or order some online from Summit/Jegs etc. I've simply experimented with multiple fluids and tried them all in my daily drivers. After a lot of fluid swaps I found the unconventional mixture of Redline and the Synchromesh fluid from Amsoil to be superior to any of them straight up. I'm not the only person who's experimented with the GM synchromesh type fluids as if you do some reading people across multiple vehicle brands and a huge range of different transmissions have seen improvements with the synchromesh fluid. While many have reported running non-synthetic synchromesh fluid hard in other transmissions requiring 75W90 gear oil without issue (and I've seen some long term results with blackstone lab testing to back them up) I feel the synchromesh fluid alone is too light to be run straight up which is why I mix mine with the Redline gear oil for the extra protection of bearings and gear teeth while still getting better synchro performance. Also the Amsoil is the only synthetic version of GM Synchromesh fluid I know of that's readily available off the shelf and mixes fine with the Synthetic gear oils from Redline.
As I noted before YMMV but I've had nothing but good things to say about it from my own use.