P55 Extreme4
i7 870 @ 3.3GHz (150 BCLK)
2x 4GB G.skill Trident DDR3 1600 7-8-7-24 (@ 1800 8-9-8-24)

Board is not accessing all 8GB of memory in dual channel mode (slots A1 and B1). POST shows 4088MB, Windows 7 x64 sees 8GB installed, only 4GB available.

All memory is available in single channel mode (slots A1 and A2), POST shows 8184MB.

Any ideas how to get the board to address all 8GB in dual channel mode?