If it's happening over multiple ROMs, you may want to test before you install anything to see if it's something you are doing. Is it happening all of the time or only awhile after a soft reset? One tool that is easy to use is cleanRAM. It has 3 levels to how aggressively it closes programs/reclaims memory and can do extra things like restart sense/spb mobile shell/etc. or schedule a time to soft reset every so many hours.
[APP]htcAddicts - cleanRAM v2.5 (RAM Cleaner) - xda-developers