God Of War Ghost Of Sparta and Chains of Olympus

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I'm not talking about frame skipping(I don't use it at all),I just mention "above 600%" just to say that my pc can give me a lot more than full speed.
I just play the game normally without frame skipping(off and auto is disabled)and randomly the speed goes down if I play in full screen WITH vsync enabled

And isn't this true "fast forward automatically enables frameskip" only if FrameSkipUnthrottle is set to true(which is set to false here)...if I set it to true,I have 1500% speed(and more depending on the location)