Good morning (or evening for some), 
 
I will try to explain this as clearly as I possibly can.  It is an issue that is extremely frustrating. 
 
I built a new PC about two weeks ago. 
 
ASUS P6T X58 
Intel Core i7 930 @ 2.8GHz 
6GB OCZ DDR3 Triple Channel RAM 
EVGA nVidia GeForce GTX 480
Windows 7 Home Premium x64  

After first booting up the machine, 6GB showed both in the BIOS, AND the OS. 
Soon thereafter, I started noticing that after leaving the computer off for around 5 or more hours, both the BIOS AND the OS were reading 4GB.  HOWEVER, PC Wizard, CPUZ, etc. were all reading 6GB 
 
After a couple weeks of troubleshooting and COMBING through forums, this is what I have come up with. 
 
On cold boot, both the BIOS and OS will show 4GB.  After a SHUT DOWN, then POWER UP (NOT a restart), the system will read 6GB.  If the power is left off for more than 5 hours, the system reverts back to 4GB being read. 
 
Here is what I have done to try to determine where to go from here: 
 
1. Ran Memtest - 5, count 'em FIVE full tests run detecting all 6GB, PASS 
2. Update the BIOS 
3. Changed speed from "Auto" to "1333MHz" (and back again since it didn't work)
4. Reseated processor (checked for bent pins, none bent) 
5. Reseated all RAM, tested all RAM individually in all allowed combinations 
6. Applied Windows updates for the fuck of it 
 
Now here's why it is so frustrating...After literally SCOURING through forums, I feel there just CAN'T be this many people having to send back parts.  Everything seems to work perfectly when the 6GB is detected!  I just don't understand and every time I talk to ASUS, they say someone will have to call me back and no one ever does. 
 
PLEASE, GiantBomb community - You have never let me down before I hope that it doesn't start now.  You guys are such a good wealth of information, some HAS to have gone through this. 
 
All of your help is EXTREMELY appreciated and I will try to stay as up to date as possible throughout this thread...some things I may not be able to try immediately, so thank you for your patience.

This is my area of expertise but have you tried the Tested.com forums? Theres dudes on there that far outweigh my experience. 
 
Have you tried booting with just one stick at a time? if not try it multiple times, sounds like you might have a dodgy module.

I've actually had the exact same problem before, and my rig is fairly similar (Core i7 920 @ 4Ghz, 6GB DDR3, Windows 7 x64 HP, Nvidia GPU). To put it simply it...sort of resolved itself. It did it the first couple of months that I got it, but after that it would just constantly show 6GB. When it was happening though, I found a weird kind of fix, I don't know if it will work for you. In order for it to show up mostly as 6GB, first of all install the latest .NET Framework, then DirectX11. Next, go to DxDiag and make sure that you switch it to the DX11 info and restart. After that, it was 6GB 90% of the time until it eventually fixed itself. Probably not all of the steps are correlated to the fix (if at all) but I thought I'd share my experience. It's actually a fairly common problem, and no clear solution is known, but not a big deal for most applications. 

Thank you both - I will still monitor this thread but also post my request in the others.

Problem pwnzrd? pwnzrd.

" Problem pwnzrd? pwnzrd. "

Okay so yesterday I needed to put some new thermal glue on the processor and after doing so, everything has seemed to been working.  I will keep this thread updated for anyone else having this problem.  Regardless, thank you all for your help!  Also, anyone else who has had this problem, please feel free to give your input!

Looking at the P6T BIOS update changes, there appear to be 3 updates that address issues with memory. So if it hasn't been resolved, you might want to try updating to the most recent BIOS revision.

Well I'm glad your problem is solved and nice rig bro.

OK...day #3 and I everything is still looking good - I'm hoping that everything stays OK.  As always, I will update as time goes by.

I was reading mobo reviews lately, someone wrote the same thing. He said when he loosened his heatsink, it would read all 6gb of ram. I think it's fixed now and it won't revert to 4gb.  
  
I googled the problem and lots of ppl are having this same problem, I guess that's the solution then, even if it didn't totally make sense to me right away. If it works, then it works because it might be blocking stuff.

I had a problem with my new PC where it was only showing half the memory in Windows 7, but was showing all 4GB in the bios. I just pulled out the RAM and reseated it and that seemed to work.

OK I guess this is day 6 and still no problems....I am so friggin hoping that everything will stay working!