You can check outside of TADST -
open task manager (Ctrl-Alt-Del select Task Manager or Ctrl-Shift-ESC)
Goto processes tab
Right-click on arma3server.exe and select Set Affinity
Right-click on arma3.exe and setect Set Affinity
Assign server 2 cores (1 and 2 if you have more than 4.. .leave 0 out of the equation if possible) then your client the rest.