Have you sanded the fin a bit to get rid of the little bumps and lumps around any graphics?
Inboard strap positions might help slightly.
If your JP has a Tuttle box, I'd try the fin from your JP (even it if hangs out of the box a tiny bit) to see if it's just a bad fin.
Or see if anyone you sail with has a fin about the same size in Tuttle that you can try for a couple of runs to find out if it just the OEM supplied fin, or soemthing else.
Hope this helps,