You shouldn' t be having a tuning problem going from right to left offset. Shouldn' t make any difference.

2215 is in the ballpark (' B' stiffness) for a 27" arrow off a hard cam 63 pound bow w/release so, even though it' s possible, I' m not too all fired ready to jump on spine as the problem. Just to be sure though, get hold of a 2216 and give that a try. If it tunes up then you know it' s spine.

What kind of rest are you using? Did you adjust the tension on the rest to compensate for the heavier arrow? If it' s a prong rest, did you adjust the prongs to fit the larger diameter?

One thing I very much dislike about GoldTip nocks is the tight double snap they put on the string. An XX75 nock is completely different, so your results could very well be showing the difference between the two styles of nock. But make sure the nocks on the XX75' s aren' t too tight.