Still stand by what I said. The amount of drag can make a huge difference in accelleration.
I get down to Monterey usually a couple of times a month (and some of my dive buddies have been talking about diving around SC anyway.) Maybe we can set up a meet-and-demo sometime (though I'm heading north this weekend, so that's out...) Might be able to come up with some ideas.
It does feel like it's drag related, that's why I was thinking it could be from the foil. just looking at the foil, it looks badly designed from a hydrodynamic point of view.. and the feeling when the boat takes off is of coming "unstuck". I'm thinking that the water may be maintaining attached flow on the foil most of the time, but then aerating when I come off a wave, dropping a bunch of drag for a couple of seconds.
I probably won't have the boat back in the water for a few weeks as I'm out of town for a while. Are you tank diving or freediving? I'm a freediver myself.