You currently have the legal right to have your child move with you out of state as long as the court order allows you to do so. However, if your ex wants to file a case to mofidy the current court order then he can do so and have your son visit with the Judge in chambers tell the Judge which parent he would prefer to designate his primary residence. It is not binding on the Court but without evidence to prove that it would be determential to the child the Court "could" make orders allowing him to stay. Also, there is no parental presumption on modification cases and therefore the grandparents could get involved in the cases as well. It does not mean the Court would override your current order it just means they could change the order. Keep in mind that this is a general answer to a general question and for you to receive a detailed answer that deals with your particular facts it would require more information from you then just can you force him to move. It would also require a review of your current Court Order.
Read your divorce decree (or SAPCR order) closely. Sometimes in the custody section, there will be a geographic restriction to a particular geographic area, sometimes not. If not, you can move him (theoretically--see below).
If there is a geographic restriction in your decree/order to your home county (or home county and contiguous counties or State of Texas), then you would need to go to court to ask for a modification in order to move with the kids. These are called relocation cases; you'd need to explain to a judge why you need to move. Work when you've been unemployed in Austin is a decent reason; a new boyfriend not as persuasive. Your son would get to give the judge his 2 cents, as would dad.
Keep in mind that this "child" is 16, not 4. If he really, really, really doesn't want to come with you, even if you have the legal right to move him, you might find him gone one day from your new place, back to his family in Texas. A session or two might with a family therapist might make for a smoother transition...?
You may wish to talk to a local attorney for more advice. What you're proposing may be an uphill battle and legal advice might be helpful.
The above is legal information, not legal advice. If you have not paid me and signed a contract, we do not have an attorney-client relationship and I am not your lawyer.
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