It's same for me, I can have several days of stability on my W500 w/ RV636 (HD
3650) and then GPU reset.

I note, the GPU never recovers, when it attempts to Xorg is basically frozen, I
can VT switch to console but sometimes switching back to X it deadlocks
completely.

I do recall eariler in 3.x GPU reset worked and it would recover. Now, it's a
lost cause.