Setting process priority to High can sometimes lose performance in Games and heavy applications.
The reason - if your system has drivers or processes that your game depends on, like audio or video render processes it needs, your Game could be taking priority from them, and since your Game is waiting on them, this could slow down the game, and create stutters, etc.
With that said, it doesn't hurt to test or try it out. For most things, this won't make any difference, and if does, often 'Above Normal' priority is probably the better choice.
PS Super Resolution can help performance significantly or enhance render quality - users can try flipping it off, but it probably isn't the problem.
i.e. - The OP problem is the game using Shader 6 features, and their system is only providing Shader 5 functionality. Since their hardware is capable of Shader 6, the problem probably has to do with the NVidia GPU driver. If reinstalling the newest driver from NVidia doesn't help, they should try an older Nvidia driver that goes back about a year. If that doesn't work, then something in the connection chain to their GPU isn't working properly - so, update AMD and mainboard drivers or reinstall them. (AMD utilities or from Device Manager - hit update driver, use let me pick, then chose the same driver - it will get reinstalled. If still not working they can do an in-place upgrade of Windows from an ISO - doing it as an upgrade from the ISO is more comprehensive in what is checked and corrected. It also gives the option to keep programs and software instead of having to reinstall them.