Hi Pat,
So, what has happened since this post:
viewtopic.php?f=40&t=4687&start=20#p35251 ? You had no motor clipping there (though their range is still pretty wide).
I'm not sure, but from what you posted it looks like "classic" vibration issue where the PID controller is basically amplifying the gyro output. I would try to tune the attitude PIDs to where you get the best control response but with as narrow motor output range as possible, as far from clipping as you can get. Until then, it'll be a "nervous" flyer at best. Reducing Tilt Angle D is the quickest approach, but it will reduce control authority and as you've found, if you reduce it too much you'll loose all control entirely. After you find a happy medium there, the other rates (esp. Tilt Angle D) can sometimes be increased to give you back some control response.
I could also build you a special firmware which reduces the sampling rate of the Gyro sensor... a few people have had good luck with it on difficult frames (including myself). Theoretically the same result can be achieved by tuning the attitude PIDs, and I'd recommend that approach vs. a custom firmware. Putting the PIDs on Tx knobs (with my beta firmware) would be the first thing I'd try since it makes PID tuning almost fun
HTH,
-Max