How is your air intake and exhaust configured on your system? It may help to know how your system is set up so that folks can see what you are working with and how they may help you improve your airflow to lower your temps.
Anything over Base/Boost clocks is perfectly normal. If you start going below base clocks, there is a problem. If your card is overclocking itself with GPU Boost, and you are overclocking on top of that, and it adjusts down from 2000mhz to 1900 MHz, you are still well above stock specs and your card is operating normally.
Please provide details on your system, to include the frequencies you are referring to.
Best bet is to include GPU Sensor tabs after gaming for 20-30 minutes, or HWInfo64 clocks. This will show actual numbers and not broad numbers or guesses.