The soreness comes from having to squeeze the ball. There could be a number of reasons for this. Span too short, thumb hole too big, too much reverse pitch, too much bevel, or any combination of these. It is really hard to tell on the internet. What part of the country do you live in? I may be able to help you find a knowledgable pro shop professional in your area.
Let me know.
Mike Austin
strikes4days@sbcglobal.net