I have had the same issue lately, and found out DCS.exe only ran on core 0 and 1 in the Task manager-Details-(rightclick set affinity)
What i did was leave affinity 0 and 1 for system and 2 and 3 for OVRServer_x64.exe and the rest of your cores for dcs, you have to do this manually each time, but if it works get Process Lasso to do it for you.
This also works on another flightsim i'm not gonna mention the name of here ;)