FS9 default scenery blurry problem

This has been talked about for some time. This problem might be easier to fix. Problem- Default scenery goes blurry after airborne for a minute or so. I do a screen refresh. Looks fine. A minute later blurry again. Happens mostly in mulitplayer with weather loaded. Older machine but never had this problem before, at least not to this degree. This seems to be default scenery... hills, trees, etc. No extra scenery has to be involved at all. No extra scenery in view even when I know I am not pointed in the direction of any known 3rd party scenery. INtel D845WN motherboard. 1.4 gig, front end bus about 400. Slow by today's standards. ATI Radeon 9600 128 mem video card. AGP 4x. 1.5 gig memory, hard drive 60 gig, 1/2 full. Power supply- 250.Settings-frames locked at 20avg frame rate- 18 even with the blurries.scenery settings all normal slidersglobal draw- massive. no change at any other setting.render to texture checkedtransform lighting checkedbilinearmipmap 4hardware rendering 5 1024x768x32no anti alias - if checked terrible frame rates.crash detect offextended texture checked.sight dist. 80 milescloud 303D cloud 10%simple cloudsadd-on dyn onno sun glareno lnes flareterrain mesh 25detail land - maxwater lowdawn/dusk draw checked.number of add on sceneries about 80.only one land class loaded I think- Columbia Gorge.No ultimate terrain or the like.Could this be a cache problem? No problems with my sceneries I've developed or my libraries I've uploaded. Mostly in multi player with weather. This can be hard on older machines but as I said this has been happening within the last few months I believe. Thank you for any help offered. Robert Lacy.