[Steve J.]

I would question the builder about cam timing, and ask for a recheck. Did you remove the O2 sensor and put the probe into the hole for the O2 sensor to check the AF ratio at wide open throttle? If the readings are at the tailpipe, and you have a CAT, then you are not "way too lean". Also, lean mixtures that do not misfire usually give more HP. Your curve seems pretty smooth to me, not indicating a way too lean condition. Note that at peak power, your AF ratio is about 13.5 which is pretty close to ideal. So, if the readings were at the tailpipe with the cat in place, you are probably rich.