It took forever, but I finally finished my run in the Shoshone challenge. Part of the reason it took forever was my schedule has changed giving me less free time on weekends, and part of it was that I never felt this one. And judging by how it ended, it shows.
I tried to do a nice cultural victory but never got it going culturally. I kept getting distracted by Ethiopian missionaries or Zulu war parties. I spent some effort liberating the Aztecs from the expanding Zulu a couple times until I just finally decided to wipe the Zulus out myself. Unfortunately, that act seems to have made everyone decide I was a good target for declaring war and found myself fighting off wars from Ethiopia (which I won handily) and the Dutch (which I won easily).
However, while fighting these easy wars the Incas had been building up technologically and militarily and quickly rolled the Aztecs then moved north against my two ex-Zulu cities. The fight was brutal and he did not have too much tech advantage, but he had a lot of forces and despite killing many of them I was overrun. Then, as I planned my revenge against the Incas with half the map covered, the Ethiopians launched a major invasion again with my army spread thin and spent.
Rather than dragging out a frustrating end game for me that had no good path to victory anymore I surrendered.
My biggest mistake? I should have rolled Ethiopia early on and burned their territory to the ground. Also, should have spent less time fighting Zulus and more time weakening the Incas when I knew they were a problem.