OK so your graphics card is ANCIENT and probably below the min spec for GTAV and your PSU is waay too close to the limit for the system. Address those points first, the RAM is not a problem, and the CPU is fine. If you want high/stable FPS then spend $$ on graphics and make sure the GPU has enough power. Remember that even with an 80+ gold psu you're only going to get ~90% of the rated output. So look at 500W at least I would say. Good luck!