Since GTA uses a single thread from your CPU, it can surely overheat. Check if your CPU fan is running by opening up the case. If it is, clean your CPU fan by unscrewing the fan from the motherboard and clean with a brush gently. Next, if the thermal paste is dried up, you should buy a thermal paste from any store/online which costs around a dollar. Use openHardwareMonitor to record your CPU temperature. It should be between 50-65° when Idle and should at max reach 80° when gaming. If it exceeds 105°, it will cause your system to slow down, and you'll find out the reason for this problem.