Preferred fluid for 4-speed trans and rear end

[Winston]

I have to put oil in the 4-speed and rear end of my 70 340 Cuda, and I was wondering what the best brand and weight oil I should use. Any suggestions?

[Chryco Psycho]

I use synthetic 75-90 for the diff
 the trans prefers a less slippery lube, gl4 rated & generally 80-90w , Redline also has a Manual trans synthetic lube as well as Mopar has a synthetic manual trans lube , Gm syncromesh is aalso a semi synthetic designed for manual trannys