No, I don't need to have the 750's full to wakeboard. The boat is new and only been in the water a month we're just figuring everything out. Filled them full to see what it did. Figured it was a weight distribution issue, like most of you said, but wanted to be sure. Surprisingly the boat does not porpoise at all.
Did look at the prop it is OJ 13.x 17.x. Is that the upgraded wakeboard prop?

Thanks for help everyone.