ArmA3 Server - Help finding the cause of lag

Our clan runs a very popular ArmA2 Overpoch(Mix of DayZ Epoch and DayZ Overwatch) the under load the server FPS drops quite significantly to the point where the game no longer runs correctly. We require someone who is experienced with ArmA2 and the relating mods along with the custom mods that have been added to the server to find the cause of the server lag and help reduce it as much as possible so we can get our player base happy again.