THANK YOU SO MUCH.
I had this EXACT same problem, and spent almost a month trying to solve it, to the point where I (might) have accidentally broke my motherboard messing with things and had to RMA it. I built it back with a friend and showed him the issue. He happened upon this post today and it absolutely fixed the problem. Seriously, I can't tell you how much this perplexed me. I'm not sure why this happened in the first place, maybe my GPU is just old now, but I'm not sure. This all started for me when I bought a new motherboard+cpu+ram, and I couldn't for the life of me figure out why it was happening. I'm not sure why this wasn't a problem before, and only happened when I replaced my motherboard, but regardless, this fixed it.
My only question: Is it safe to run my GPU in power state 1 all the time? I set power state 1 to 300mhz, which is what state 0 was before, but I'm currently planning to leave it there indefinitely.
Again, thank you SO much.