Aircraft Textures Disappearing Over the Ocean

Hey guys,

I just recently started having this issue in FSX. On long haul flights over the pond, no matter what aircraft i'm in, the textures disappear around the aircraft. It usually happens a couple hours into the flight. I'm confused with why its happening because I have my CFG tweaked according to Bojote's Tweaker online, and I am also using an external frame limiter to keep the frames in check. I have tried flights with and without the tweaks but the problem persists. I was under the impression that the "HIGHMEMFIX" should have taken care of texture problems. More importantly, it seems to happen when transitioning from day to night. Any input would be greatly appreciated. 

ASUS P8Z68-M Pro motherboard

I7 2600K o/c 4.5 ghz

Nvidia GTX460

Corsair GS800 PSU

FSX SP1 and 2