video games stuttering

I have a really big stuttering while playing fortnite My PC Specs Are : AMD HD Series 6990 intel I7 cpu 950 overcloacked to 3.80 ghz 16GB RAM DDR3 Windows 10 pro my settings in fortnite are low and the same in amd radeon settings my resolution is : 1366x720 in fortnite my fps : 60 all that...