Alrighty, bumping the thread because I believe I've isolated the issue today at a Miata Techday meet (which funny enough my engine died again on the way to. All of a sudden, "Oh **** my power steering just went out. Wait, no my engine died.") We think it's my fuel pressure regulator that's causing it. Here's a pic to show the Jackson Racing model.
With the low boost I'm running, I really don't think it's worth it to invest a bunch of money in a MegaSquirt and tune it. I think I'm just going to get another Jackson Racing one for around $100 off a guy that has an extra. Hopefully that'll solve my issue. How easy is it to remove and install a new one?