Texture refresh

Hello - I've been diving into the mysteries of texture refresh, unsuccessfully. Here's my test case: parked at the gate at KPHX. Textures come up sharp and clear on terrain, buildings, aircraft. After about 20-30 seconds, the whole scene refreshes, may go to gray objects for a bit, then comes up with blurred textures on aircraft and buildings. If I hit the alt key the sharp textures are reasserted almost instantly, so they're still in memory somewhere.I've got a lot running: SimFlyers KPHX, F1_727. I have ActiveWeather online. I'm using FSGenesis mesh and landclass. In the 727 I have put in RXP weather radar and replaced the MS GPS with the RXP GNS530. I've installed the CIVA INS. Sounds bad, but this ran okay on my "old" machine, an Athlon 3000 with a 5950 video card.But the new machine is almost as big as they come: Athlon64 FX53, MSI Neo2 Platinum with nForce3, 4GB DDR 400, nVidia 6600GT video card so for this refresh thing to happen I probably have something configured badly.Anybody know what prompts the system to refresh textures (and how it decides which detail level to pick for buildings and aircraft)?Thanks -- Dick Bixler