3.99 usable ram on the X58 motherboard
There have several posts in the X58 section about 3.99 memory usable issue. What I’d like to do in this post is make a troubleshooting template to assist in troubleshooting this problem:

1.   Set MCH Strap to DRAM Ratio, which is under frequency/voltage page of bios’s later than version 73 on x58
2.   Change the TRL setting to +2 under the memory features of bios’s later than version 73 on x58
3.   Make sure you are on a 64bit OS
4.   Try increasing Memory Low Gap
5.   Verify each stick of memory and each memory slot
6.   Remount the CPU and verify that there are no bent cpu pins (Do NOT overtighten the CPU cooler!!!)
7.   Verify that you using the latest bios that is available for the motherboard
 
Example of an EVGA X58 classified motherboard with bent pins:  
   
http://i516.photobucket.com/albums/u321/robert3892/IMAG0012.jpg