title_body: Why does motor not want to go above 2/3 thrust?
upvoted_answer: It was the battery.
  Bought a new battery, charged it, all 3 lights turned green, and motor/esc has no trouble going to full thrust. Lots of power now, so that should really help the plane fly.
  Problem solved!
  And on the bright side, I get to tear apart the broken 3s battery and see how to fix it or turn it into a 2s. I'll probably put a question on electrical engineering SE about that later.