First of all sorry for my broken English, i'm trying to fix this too
Did you managed to fix this issue? my GPU is behaving the same! i have researched a lot without luck.
all i know atm is:
our GPU are throttling/downclocking because a Power limit as you can see in your screenshot right next of "Limits: Power : 1"
i think is a Hardware problem since i've tried almost everything, my last hope is buying a new PSU.
Tanks in advice!