If you want an alternative to GM (I can see why you might want to, but I'd be curious to know how many people see it as a problem), "referee" works well. Has an old-school flavor, and because it's an old term it won't really raise any eyebrows or "why don't you just use game master?" questions.

I'm curious as to the reasoning here. I know the word "master" has some seriously negative associations when opposite the word "slave", but that's not the case here. Nobody that I'm aware of calls D&D or other RPG players "slaves". If anything, a good GM is there to serve the players, not the other way around.

Edit: I support replacing usages of the paired words "master" and "slave" so as not to reference the very real history of slavery. I'm also totally fine with using "referee" instead of "game master". But I'm concerned that other senses of "master", like "master craftsman" or "gold master" or "game master" which refer to mastery (of a craft or some such) and don't (to my knowledge) connote "master/slave" are being lumped in here.

I've wondered about that myself. I did swap out "race" for "species", but I don't know of a preferred term there.

No, because it is a non issue. There is no need to replace it.

GMs develop the narrative that players work through, so why not call them story tellers or narrators. That would be a more literal description of their role.