Make sure you have your driver up-to-date because if they aren't sometimes your FPS will be capped and, in your case, may be bugged. Also, try using start perimeters to make sure Arma has access to use more ram and more video ram. This may fix it, or you may just need to re-install.
Been having connection problems all day on the Olympus Altis Life servers. Skins won't load on vehicles most of the time and bad FPS when normally I get around 50. Just me?