Has anyone used Amsoil synthetic Transmission lube 75W-90 GL-4 in their 1969 4 speed?

When you pulled the tranny apart...what did you find? The reason I asked was because I used the wrong weight in a Honda transmission once and it lasted a very short time. Meaning that if it was the Amsoil 140 maybe it didnt lube the parts like it should have. With that being said..maybe it more of the salesman instead of the product itself.
I have been using the Amsoil in my NV4500 Dodge Cummins transmission for the last 100k and its doing fine. As you may know that this transmission calls for the Castrol Syntorq or they say if anything else is used...it will cause issues with the transmission. Still waiting on the issues to start. Transmission has 271k on it.

Rick