Fallers is the generally accepted fandom name, but I've never really liked it. Gravitationer sounds like it's referring to प्रशंसकों of the याओइ मांगा Gravitation. I just tend to call myself a "fan of Gravity Falls".
Maybe we should be called Gravallers. लोल Gravel. But really, I don't know what to call the fandom. Graffies?
Gravity Fallers? Big Dippers? Grunklers? The seeing eyes!....sounds like a band name. Bystery Foots! cuz there are lots of mysteries in gravity falls and one of them is a hidden bigfoot in the theme song. Idk. just pick one.
Faller works for me, it's what's listed on TV Tropes and I can't think of a better name for our fandom. Gravitationer sounds nice, but if it's associated with याओइ in any way, I'm not interested. All of of the other ones I've heard seem too obscure, या too unidentifiable.