I would definitely swap the tail motor. It sounds like the brushes are binding and it's very difficult to "nudge" while in flight. By lipo I assume you went with 3s, and by doing so had to change to the 8 or 9t pinion. If you didn't change the pinion that would explain your tail problem. They burn out very quickly on 3s with a 10t pinion. Also be sure to add the heat sinks if you don't have them.