Texas is in great economic condition however, it by no means would be one of the top four or five economies by GDP in the world.
Unfettering itself from Washington's crazy policies, unshackling gas & oil from the enslavement of the Greens, practicing free trade, and freeing her citizens of high taxation would pretty much ensure that within 10 years, it would be.
Even today, Texas, Our Texas, is the second most populous state of our current 50.
According to Wikipedia Texas would be 10th. Right after Canada and ahead of Brazil.