I'm suffering from the same issue with my built motor. Only I have a 3076.82 running with a cosworth FMIC, cams, heads, and ALL the goodies. My boost tapers at 5700 and HP follows it. My tuner/builder thinks it might be the EWG up-pipe. We have a 20lb spring in the ewg now, which helped spool, but the taper remained unchanged. Totally stumped