Not sure if it's a lack of pressure from the fuel pump just yet. I did some data logging on a couple runs and it appears that the injection timing is decreasing at a certain point causing the AFR to lean out. I'm not sure why the injection times would decrease; regardless of the pressure it seems the timing should continue to increase with the boost. Here are a couple graphs showing the decrease in injector timing and AFR change:
Z4m run3graph by
M detaR, on Flickr
Z4M run4graph by
M detaR, on Flickr
Z4M run5graph by
M detaR, on Flickr
Hope to hear back from VF after the weekend.
EDIT: AFRs fixed...
Z4MrevAFR by
M detaR, on Flickr