My RAM :(

Ok I built my machine back in Feb. Everything runs awesome! Except my ram! To me this is very odd - Sometimes I can change the timings and run the parts at their rated DDR3 1866 speeds other times I change the settings and Windows (or the Motherboard ???) rejects them and I have to let the board clock them down to 1333MHZ or 1600MHZ. - Which is against the point of me trying to get faster RAM? :p The board and the RAM both support a Dual Channel config.

What am I doing wrong?

My build:

AMD FX 8350 at 4GHZ water cooled with Cooler Master Seidon 120V 
Gigabyte GA-990FXA-UD3 rev 4.0 Motherboard 
G.SKill Sniper Gaming Series RAM DDR3 1866 - 32GBS 
Kingston SSDNow v300 240gb SSD 
Western Digital Blue 2TB Sata 3 6.0Gbit\s 
Cooler Master V850 - 805W power supply - Modular 
ASUS Blu-Ray burner - 16D1HT 
Cooler Master HAF 932 Advanced Full Tower Case 
BitFenix Recon 5 channel Fan Controller 
2X Sapphire Tech Vapor-X R9 270X GPUs - Crossfire - 2GB GDDR5 256-bit Mem Interface 

Are you using cpu-z to look at ram timings? When you say change the settings are you overclocking?

I used CPU-Z to get the timings the RAM reports for that speed and no I am not overclocking.