game play drops to super low resolution settings

running on my mac pro tower when i go into game play it drops to approx 800x640p on this lovely wide screen monitor i have defeating the point of running on hdmi. i can not for the life of me find an option to switch my resolution in or out of game play. i use this computer to run projectors at resolutions of 5760x1080p with a 1080p monitor for controlling and have played this game at 5760x1080p(on projectors) using a friends windows machine we built for the same purpose as this comp was however it seems that i have the absolute worst possible resolution setting in this game with no option to change it? WHY? plz give us back resolution options