Hello.
Try to create a separate profile for GTA 5 in the driver settings. Experiment with the shader cache option (on or off).
I do not play GTA 5, however, in the game Watch Dogs 2, disabling this option allowed me to get rid of serious friezes. And in the Black Mesa game, on the contrary, inclusion helps.
However, this did not remove the small periodic FPS drops. But playing became much more comfortable.