I can help you with this one. Its so simple you'll smack yourself in the head for not thinking of it. Straight Ammonia!($0.99 at any grocery store) Put some on a rag (cloth works the best) and wipe your window down really good. Becareful not to get it on the paint because it will strip any wax that you may have on it. Yeah, it may take a few passes but it work great! Use it on your windshield and you'll see a big difference. When your done with the Ammonia its a good idea to clean the window with something else or just wash your rig. You don't want that stuff hanging around stinking.
Oh, and if this doesn't work then you have some funky stuff on your window. Let me know what you think of it.
