Thanks to all for your informative responses. Looks like my gut feeling was correct. I'll order a Center Diff once Mantis gets the next ones going. (I checked the site today and it didn't look I could order one now.)

Looking forward to getting this thing running consistently. First day on the track the stock plastic hex wheel hub melted to the bearing holder and ended my day quickly. I've since installed the aluminum ones to resolve that issue. Next day I had issues with my steering. Took me a while to figure it out, but I believe my servo was moving (b/c my screws weren't tight enough) so my center point kept moving on my while driving. That, and my steering end points weren't dialed in correctly. So when I was turning all the way right/left, the a-arms were actually flexing pulling my loose servo right to left. I'm hopeful that after fixing all that, my next time on the track will be more than a couple laps!