Hi ChrisCP3, thank you for sharing your inquiry.
As far as I can see the game does not seem to be lagging. Still, you may try running the Windows* Experience Index and monitoring the cores usage when the processor is being assessed. Windows Experience Index for Windows 8.1
If all cores are being used then it probably is a software application issue; otherwise I would suggest verifying that all cores are enabled in BIOS as well as in Windows* msconfig; the option “number of processors” should be unchecked, as it is by default in the Boot tab. There is also a way to check if the game is allowed to use all cores with “Set Affinity”, when you right click the (exe) process of the game in Task Manager