In fact, I was leaning her out as I started with 10.9
I wonder if it's not something as simple as carbon fouled plugs after having the mixture in the 10s.
Many years ago when I ran a hot turbo'd nissan race motor I frequently would carbon foul plugs from running too fat. Symptoms were similar to yours.
Did your motor ever pull clean to 7000 with boost since installing your efi?