The federal tax on your gain will be the same either way, 15% and 20% (because the amount is so high).
California does not have a specific capital gains tax rate, your gains are taxed as ordinary income at a rate of 10-13.3% at your income level (assuming you liquidated the entire gain all at once.) That's way more than the 3% additional investment tax.
While I am not a professional tax advisor, it seems like you would save about $100,000 in taxes if you liquidate your stocks and realize your gains while you are still a Texas resident. Even if you turn around and immediately re-buy the same stocks (because then when you sell them later in CA, you will have reduced the amount of gain in CA by taking most of it early.)
But you should definitely find a good tax planner. And you may also want to think about low tax investment strategies that might make sense living in CA.
