If you still got warranty, just send it back to your supplier. They've send me a brand new one and it works like a charm. I've been through all the same shit as you with gigabyte support and trying to find answers online. Just send it back and it will save you hours of work.
Couldnt do it and still cant, because its constantly under load, if I send it back, I'm 100% sure it will take more than 2 weeks and that's an optimistic estimate! I'm sure they won't do anything about it.
couple of weeks ago, I noticed all of a sudden, the fan RPM reached 3000/4000 or so, it spun so fast that really scared me! the sound was extremely high and as if a jet engine is spinning inside my case!! and then it quickly was turned off! all 3 of them!
The GPU temp quickly hit 98 99 C and I had to quickly terminate my long-running experiment and navigate and run Gigabyte Extreme Engine and set the Fan on the turbo mode and it started working again! and the card wasn't even overclocked!.
I dont know what would happen if I weren't there, at the very least I'm sure that would have probably fried my GPU for good!
This is serious, I have never seen anything like this before! anything!