So I think I've finally found my title (or at least narrowed it down to 2 options)!
42,000+ words in and it finally came to me.
My problem, I think, was that I was trying to avoid giving away too much of the plot in the title. I realized, however, that to some point that can be a good thing. Additionally, my title choices don't give away the series plot and instead focus on the events of the first book.
So hopefully by August I should have "Hellhound's Revolt" or "The Cerberus Rebellion" on e-readers everywhere!