Bottle necking isn't so simple and there is no way we could accurately tell what's bottle necking. To find out yourself, download a program like MSI afterburner and setup the on screen display to show the FPS, each CPU core usage, and GPU usage. Whichever is at / around 100% while the FPS issues is likely the limiting factor.
Though I don't think the problem exists in either the CPU or GPU. "texture loss-1 second freezes", from that, it is really looking like storage lag spikes. Loading new terrain/textures requires the HDD/SSD to load, and if it's slow doing so, you will receive short FPS drop.
What is your storage set up ( are you using HDD or SSD, what is GTA 5 installed on)?