These Stutters/Hiccups are occurring due to low transfer rate of the HDD. I had a 4GB RAM too, so it stuttered like hell, but gave always 40+ FPS, but I got the solution
SOLUTION:
Warning: Please backup before editing.
Edit the "settings.xml" present in Docments\Rockstar Games\GTA V with any text editor and set the values as shown.
LodScale value="-0.500000"
PedLodBias value="-0.500000"
VehicleLodBias value="-0.500000">
CityDensity value="-0.400000"
Now Save & Play the game.
You can play with the values & set whatever suits you best.
There is a GTA V Low Graphics MOD too..
https://www.gta5-mods.com/misc/gta-v-config-for-1-5gbram-or-more