If you do a search on here you will find a lot of threads on this subject and a lot of differing opinions. But there are a few things that the service manuals tell you. First, GL-5 is for differentials and is not the best choice for your tranny. Especially the GL-5 with Sure-Grip or Limited Slip additive. That was true 50 years ago and is still true today. Now that doesn't mean that putting Gl-5 in your tranny will smoke it, it just means that it is not formulated for it.

GL-4 is the lube designation you want for your tranny. And it can be difficult to find nowadays. And there are different weights of it, too. Correct me if I am wrong, but I think that our trannies want 80/90. The last time I had to find some, all I could find was 140. The tranny shifted real stiff with it, so I just kept cutting the gear oil with ATF until it shifted smooth, Ended up about 50/50 ATF and 140 GL-4.

I think if you look in the original service manuals, ATF was called for in colder climates. I personally do not like straight ATF for summer driving, but I am sure that someone will disagree. For me, a GL-4 with a viscosity that is not difficult to shift until it warms up is the way to go.