I was only really remember the book 2 to book 3 wait. It was actually less time than Korra.
But then they took a long break after Day of Black Sun. I remember that people were desperate for new episodes, Canada managed to air The Western Air Temple and The Firebending Masters right after DoBS while the U.S. had to wait. After that it was a couple of months and a shady site that will not be named had a user who got a hold of the Book 3 Volume 3 DVD, which had the Canadian premiered episodes as well as the never before seen Boiling Rock eoisodes. The guy managed to rip the DVD on his own and everyone got to see Boilng Rock.
And then began the long wait till July 2008. That's when Nickelodeon decided to air the epusodes the US had not gotten yet along with the final set of episodes. Was a crazy freaking week which ended with Sozins Comet on the Friday that The Dark Knight came out on. I'll never forget that day, probably the most mood whiplashy day ever seeing The Dark Knight at midnight, watching Sozins Comet in the evening and then finding out that my aunt died and having to drive to Montreal in the middle of the night.
Ah memories.
that sounds like the nonsense that happened to gravity falls.