Hi Jim,
Without having read the text of your book, I'd have to defer to you as the expert on an applicable title. Your ideas of "Gold Medal Mind" and "Victory Mindset" sound good. I don't know about a subtitle, but if you do use a subtitle I'd suggest one that's more of a straightforward/uncreative description of what the book is doing ("How to Think, Train, and Thrive in Your Sport" is relatively straightforward, but "Applied Psychology for Athletes" would be even more direct). Hope this helps!
-Tori