gta needs at least 8 gbs of ram, that is why it reads alot the hard disk, it is using pagefile, ram on hard disk and that is slow as you see and reads the
add more ram, 8 or 16 gbs, remove those 4 and 2 ram modules and put more ram
the entire specs include psu, mainboard, ram, cpu, gpu, all the specs, not just two things
all parts are involved when playing games, especially gta that is cpu and ram intensive