If you find a person breaking into your vehicle, while you are at home, there is no controlling case law that says you are allowed to use deadly force against a car burglar. You could be put in the position of being the test case for whether or not your actions are allowed under Texas law. Remember, use of force must be reasonable, it has to be immediately necessary, and it should be proportional to the amount of force that the person is committing against you.
One issue is the misrepresentation on the Internet about the “castle doctrine”. The “castle doctrine” is not a law; it is a concept discussed largely in the media. Section 9.41 of the Texas Penal Code is what governs when deadly force may be used to protect property. So, while holding someone at gunpoint is potentially something that you are allowed to do when you find someone burglarizing your vehicle, keep in mind that the ultimate authority on whether or not it is allowed is a jury of your peers, or a judge. You decide, is that stolen pair of sunglasses worth all of that? Prevent theft, lock your car doors.