As the tittle says, I have a lot of stuttering no matter what configuration I use. Even in the lowest settings, 720p I have it. I tried to fix it through the Nvidia control panel and even tweaking some .ini archives but nothing worked.

My PC:

GTX 960
i5 5470 3.2GHz
8GB RAM
1TB HDD

You don't have enough RAM to run the game, your OS and everything else that's in the background. The game is having to rely on virtual memory, that's where the stuttering is coming from.

I close almost everything, there is no way to fix it then??

Of course there is: install more RAM.

http://en.cdprojektred.com/support/tw3-system-requirements/

They say that 6GB is required as well as recommended. According to this, your 8GB should be more than sufficient. Sure, more RAM is always helpful as disk cache, but you are talking about constant stuttering, aren't you. Do you have mods installed -- that's the rightfully standard question I would have expected from Hickory (greetings, mate, you've been most helpful), like, texture mods that might fill up your Video RAM?

My first guess, though, would be an anti-virus tool running in the background. (You'd be surprised how well MS Office runs w/o an AV -- even better than LibreOffice under Linux. ^^)

So: Disconnect from the net, disable the AV, reboot, and check again ... if you haven't done so at this point.
And check the Task Manager about what might eat up your CPU cycles and/or block the file systems. (To me, a real show stopper for anything under Windows is the file indexing mechanism -- it's the first thing I disable)

My second guess is, that, well, your CPU seems to be near the lower end of the spectrum. I have no experience with that, I'm afraid (ahem, with this game and this my rig ^^).

In my limited experience, tweaking by means of the Nvidia control panel or the tool provided by the 3d gurus works only if you know what exactly you are loooking for.

Just guessworks. :/