Your GPU is most certainly not broke. It would be broke if you experience crashes, blue screens, total freezes requiring reboot and the like.
If anything, then your GPU is just overloaded and maybe in throttle mode (or the CPU).
From the log you provided I read the following:
GPU fan is spinning, it holds the GPU at about 70°C at start, Consuming about 75-78 Watts. The column CPU_UTIL shows some irregularities half way down. After that Power consumption doubles (130), Fan speed increases and temperatures jump from 70 to 77 and do not go down till end of log.
Did you start the log shortly before starting the game maybe? Or is this log from playing some minutes in?
-- I wonder... is CPU_UTIL maybe CPU_UTILIZATION and the 100 means 100%... then your CPU is at full max all the time. Use the task manager or other tools to monitor more closely if other processes are causing CPU load.
Here is what you could do:
Lower the video settings, check if the FPS are stable with that. If so, the GPU or CPU is limiting.
Standards: Check the game forum for similar issues. Update Adrenaline. Hope for a driver update for Horizons 2.
Just to make sure: Try restarting the system (I assume you did).
Do you run some overclocking stuff? If so, disable that and retry.