Do you diligently practice them slowly, but it doesn't seem to help one bit?
When you rehearse with the group at tempo, you can't seem to even move your bow as fast as it needs to go--and forget about the left hand!
It is almost as if your brain melts and you are paralyzed by the sheer rapidity of the notes flying by...
Sound familiar? It does to me!
Here's a video all about what it means to "fake" in orchestra:
Happy (fast) practicing!