At this point the only things that come to mind are that perhaps your cpu is throttling your ram speed (if its dirty or overheating something along those lines) or that you have 2 slots of ram and one of your sticks of ram are bad.
Is this a Laptop or a Desktop? I quickly scrolled through, but I did not see mention of it.
I'm at work right now, and about to get busy, but the additional info might help others attempt to diagnose the issue.