Tex. Tax Code § 152.081
The taxes imposed by this chapter do not apply to the sale or use of a motor vehicle that is:
Acts 1981, 67th Leg., p. 1593, ch. 389, Sec. 1, eff. Jan. 1, 1982.
Amended by Acts 1997, 75th Leg., ch. 165, Sec. 30.256, eff. Sept. 1, 1997.