Um .. gotta roll that back. I only had 6% max hills going home, the 8-12% are on the way in to work only. It was squeaking again this morning. But, I did notice that it only happens in the biggest ring in back, shift one gear over and total silence. I was not noticing this before as I am always in the biggest ring on 8+% hills.

I think the limit screw may need some adjusting, not sure why it is squeaking from that but I can't see what else could be the cause. The chain looked like it might not have been perfectly centered on the teeth so I tightened the screw a bit to get it centered. If this doesn't do it I will take apart the cassette, and lube and re-install the rings. Other suggestions welcome..