I've been having the same issues as OP and it's driving me crazy (using an EVGA x58 sli). Tried reseating, slightly loosening pressure on cpu, setting it to 9-9-9-24 1600, flashed BIOS twice, and a bunch of other stuff I can't remember. It goes back and forth between listing 6.00gb or listing 6.00gb with only 1.99 usable.
There's no memory remapping feature on this motherboard too. I tried playing around with a memory low gap setting after reading http://www.evga.com/forums/tm.aspx?m=403758&mpage=1 but I don't think that's quite right since I've been able to run all 6gb before.
Also reseated the CPU and checked for bent pins. Didn't see any, and I REAAAALLY don't wanna install the heatsink again to make sure
edit: just used the handy clear cmos button, seems to have work. Clearing cmos resets to motherboard to default, including any BIOS flashing right? Maybe I just won't flash it then lol
Noticed my memory use creeping up, and even had Windows spit a warning at me about it. I have 8gb, and checking processes and such seems to show it's all there. However, when checking how the memory is being distributed, I'm seeing like 5gb being sucked up by what windows calls Modified Memory. Looking back at process, everything I have running is lucky to top 1gb at the time. Not sure if my BIOS has the remapping option, either, but any ideas what may be causing this otherwise?
First noticed it after installing the XIV beta and Adobe Illustrator. Dunno if it's one specifically or some combo of things just eventually messing up. If it makes much of a difference, I tend to leave my PC on most of the time, no sleep mode or anything. Win7 64bit, too.