Awesome, thanks for the tips.
I revisited the TX setup and I had mistakenly set it to 2-servos when it should be set to 1 servo.
Got it all trimmed out on the TX, then went back and adjusted the ball links to get the same level of trim mechanically, and now I have it set for perfectly level flight with a fresh battery with no trim dialed in on the TX. As the battery degrades, I have to dial in trim to keep it perfect, but considering how short the flight time is, I'm not going to worry about it.
Now to just get some more batteries...