I don't think the VRAM indicator in GTAV is even remotely accurate.
Yeah mine is miles off also, i wouldnt worry bout it

As long as it runs smooth and looks nice its all good.
The game is so undemanding ive acatully dropped my cards down to 800/1250 which is my energy saving profile i use in wow, cause im getting cooked in my room here my pc is kicking out so much heat. As long as it stays around 60 fps i dont mind.