I think you're misunderstanding WHAT ReShade and SweetFX ARE. Ready:
"ReShade itself does not come with any effects (apart from the example shader). It's a platform to write and inject your shaders everywhere. Either download the ReShade + Framework pack or head over to the presentation section in the forum to download some standalone effects users made with ReShade."
In other words, ReShade is just what runs/applies the effects. SweetFX is, as I understand it atleast, a compilation of shaders not specifically optimised to any particular game. Im not 100% about this, I haven't downloaded it myself, I went through the +framework download.
Even if im wrong about SweetFX, the basics are still the same, and I recommend you try looking for GTAV in the User made Presets, found Here; http://reshade.me/presets
Theres a link explaining how to use a preset at the side, and at the time of writing this GTA V has a preset on page 14.