I think the "towards the end" part is the misleading one. The software has no idea where the end is or it would just jump there. Since the run took 4 days slowi

I think the "towards the end" part is the misleading one. The software has no idea where the end is or it would just jump there. Since the run took 4 days slowing down due to throttling would happen pretty fast as the card reaches a thermal equilibrium. Certainly wouldn't take days to do it. It's more likely the explanation above of something (not heat) accumulating over time and slowing down the processing.