I'm still on the fence on the GM stuff which it might affect the clutch type diff.
I'm not sure about you but I've always used what Comptech recommended with Redline MTL which I think may now be MT-90 manual transmission fluid. Stuff works great. Shifts are as smooth as ever and especially from 4th to 3rd and then from 3rd to 2nd when needed without any hesitation or resistance or grinding. I've done enough track events in all temperatures with this stuff and it works as promised. Give it a try.
Al Terpak