White Aircraft - PMDG 737600/700

Hi,I recently converted to FS2004 and almost at the same upped my RAM from 256mb to 1gig. The difference was fantastic - changing views was instantaneous and the whole thing was much better to fly. Funny thing is - I'm convinced things are slowing down again. I'm sure when I first upgraded that the views changed instantly including aircraft paint jobs. Now when I swap views, it changes straight away but I get an unpainted plane for a few seconds. Is it me or something starting to slow it down again and is there something in FS2004 that needs to be cleared out now and again. I'm using VFR scenery and British airports so i also wonder if its now trying to automatically load up higher resolutions now that I have better hardware as I haven't changed any of the sliders for ages.I've tried defragging and using disk clean - any thoughts ?FS2004Nvidia 5700 LE 256k graphics cardWindows XP SP21 gig RAMNorton Anti-virus