FS9 Planes in FSX

Hi guys, I noticed when using FS9 planes (eg. a POSKY 738) in FSX, the textures seem to lag a bit when switching from the cockpit view to outisde view when after long time. They seem to load in sections, from white or grey to the livery paint. How can I save the texture files so that they don't do this like the default FSX planes?