This appears to be a bottleneck...The biggest bottleneck I have ever seen in fact. Looking at the picture you have of gta it appears that you have all of your settings turned to the lowest. With 90 fps I would think that it is a cpu bottleneck as gta is very cpu intensive for certain builds, a 1080ti would get far more fps on a non-bottlenecked build. That is the framerate I would expect your cpu to be limited at, however, even at the lowest settings that gpu usage seems way too low.
To test if it really is a cpu bottleneck try lowering the cpu clock speed(making sure you know what you are doing). If the framerate lowers when the clock speed is lowered then it is a cpu bottleneck, if not it is something else that is bottlenecking your system or the drivers are somehow conflicting with the game(it was made in 2014)