I would say your power shortage is due to your Polyquest 1900mah battery. I normally fly with my TP2070 extremes, but used my TP2100 pro-lite for awhile and experienced what mentioned above. I realized the TP2100 could not push the amps required by T-Rex motor and esc for long, evidence was nasty tail wag and 5-6 min flights and a very warm battery. When I switched back to the TP2070 no power problems and tail wag disappeared and now I get 8-10 min flights.

Check the C rating. C rating of TP2100 is 15C/20C and the TP2070 is 25C/50C as you can see the TP2070 can handle higher amp draw.