Weird behaviour FSX

Hi everyone,I am just about at my wits end here...FSX is behaving strangely. At the end of long flights I am getting graphical glitches in FSX when I either ALT-TAB to the desktop and back to FSX or even when I use the menus in FSX. The whole aircraft panel disappears, or the screen flashes black and white, or the screen turns black. The AI aircraft are sometimes see-through. Then I cannot use the menus in FSX anymore. This typically occurs at high-detail add-on airports with detailed aircraft. I have the OS and FSX on separate physical drives, and have tweaked as per Nick N's guides. There isn't anything running that shouldn't be.Temps of CPU indicate 50-52 celsius and the GPU is between 50-55 celsius. I don't think that is particularly hot?? The CPU and GPU are slightly OCd but I have reduced both to stock standard and still see the problem. process explorer indicates a WS private size of around 1.64Gb and a virtual size of 1.9gb for fsx.exe.So far I have reduced things like the AI settings, scenery and autogen, texture resolution. I have tried reducing texture sizes in UTX Europe and tried switching it off completely to see if that helps but it doesn't. Slider positions are as per Nick's guide except traffic which is 0% because I use Ultimate Traffic 2, and the scenery & autogen which are at dense.Tried going to 185 drivers but that made it worse. System specs:Vista 64bitAsus P5E mobo with 4Gb RamGTX 250 1Mb with 182.50 driversX-Fi Xtreme Gamer sound cardAnyone got any pointers?ThanksJonathan