Memory Madness please help

Hi guys so gotten to the stage im optimizing my project.
when loading the mission my game uses 230 first time loading of memory then the second time uses 430mb which is mad. this slows down start time but the worrieing thing is that the game uses 100+mbs while running, the frame rate is good 60+ in release but ocasionally jumpy in random areas round map which suject not specific model.

what ive done...
added flying vehiles
added loads dts's but used severe LOD to keep fps up..
added models loads

what way can i tell what is eating up what memory and is there a way to keep thing out side a sertain radius out of virtual memory.
visibility doesnt work as i increase to 1000 the mem usage is 200 mb and then reduce it to 1 then the mem usage still 200 mbs.

i read about the tree();
but not sure what it does

does anyone know how to make a "me no see" ie visibility the samea as comp not see engine not see (cpu comp) whatever you would like to call it.

Again as alway i appreciate you time and any help sorry for making this long....

cheers