My graphics card became lazy

[Nitestick]

I'd say it's likely the power supply, it may say 800W on the label but it's reliability can be questionable. I recently sold a desktop that had a 5 year old 480W PSU in it that ran fine the whole time including at it's peak running on an SLI system with a quad core, 4GB of memory, a tuner card, 4 hard drives and 2 DVD drives; PCs don't need as much power as you might think although current graphics cards can get mighty power hungry.

"according to CPUID my graphics card is getting 1.05V of VIN0 Voltage..."
If you can find out what it's supposed to run at this may be a good indicator, being undervolted (unless deliberate) indicates that it's being underpowered.