Bad Fps After Reinstalling Fsx

Hi,

i have a strange FPS issue that i cannot solve by myself and i hope someone can help me.

I reinstalled fsx because of some scenery problems and now the frames drop after using FSX for 20 to 30 seconds. I have a low to mid-end pc but i managed to get good fps with both the 737NGX and the 777 with moderate fsx settings.

I use the vanetubu site for fsx.cfg tweaking and the fps limiter set to 30fps. When i start at fs dreamteam's klax with the 777 in virtual cockpit i get like 23-29 fps at the beginning. Everything is fluent. After 20-30 seconds the frames drop down and when i push the trottles fsx is lacking (almost down to 5 frames). And what never happend before is that the frames remain low even when in the air flying far away from the detailed airport.

Does anybody have a clue what is causing this? Is maybe a certain tweak causing this? I wonder because the frames are high at the beginning and then they drop.

Thanks in advance for your help!

Chris