You know what. I had a similar problem. A couple of things to keep in mind and look over.
A. There is a guide to keep performance smooth. No LARGE objects.
If it's bigger than your screen cut it up.
Don't over draw.
.... and so on. I suggest checking the guide.
B. On rare occasion a Layout can go bad. I had a game i was using for C2. The main menu had only 5 objets. None of them bigger than 256x256. No physics, not intensive processing. in fact only one of the objects moved. Yet the main menu ran at best 1fps. On the rare occasion that you could get tot he menu buttons. Start a new layout. The game ran fine at a nice 30fps(on mine) 60fps(on most others). It was really just that one layout. Even though the main game play had more objects on it moving with collision detection.
If was for some reason just a bad layout. I can't identify why, but it was. Upon creating a new layout. It worked so much better.
Also constantly test on the hardware after every few changes. that way you can reverse any change that kills performance.