I had never installed GPUz before, I always used it as a portable exe. So the reason is logged as number 4 and in the graph it shows as Vrel.
EDIT: I figured out what was wrong, this is my first Nvidia card and things work quite differently from AMD cards. Basically I thought that the value inside the voltage table for each clock speed was already set so let's say CLK 74 was set to 1.128 I though the the GPU would automatically switch to that frequency once I set the clock in afterburner but that's not how it works, basically that is only the max value and the GPU doesn't use it unless you push the voltage slider in afterburner all the way to the right.
I was basically voltage starving the gpu, now with the voltage slider all the way to the right GPU z doesn't report Vrel anymore and the GPU doesn't downclock. However, the bios still behaves in a strange way, when Vrel occurs shouldn't it drop to the lower CLK voltage table? Mine goes straight to 1.190 v, it picks this arbitrary voltage out of nowhere, non of the voltage tables in my bios are set to 1.190.
How do you guys determine which is the lowest stable voltage with nvidia gpus?
With my 7950 I used OCCT error checking and I gradually lowered the voltage until the first error showed up and then I used to set the voltage on step above the one reporting errors and I tested it again until I found the lowest stable voltage. That card had only 1 clock to worry about but here there is an entire table to take care of, do you know any convenient way to find the best voltage for each CLK table?