Memory usage

[rev800x]

OK. After I soft reset my mogul is using 60% memory. After I use the phone for a while it goes up to 75% memory usage. Why does the memory get used up even though the apps. are totally closed out? And it won't let me run Garmin XT and audio manager at the same time. If I open XT and then audio manager, XT gets shut down. If I open audio first then XT, audio gets shut down. Is there anything I can do to free up more memory? I ues a task manager to close unwanted apps and free up as much memory as I can but it still stays at 75% memory unless I soft reset.