Right today if Texas seceded claiming all federal assets within it's boundaries, relinquishing all financial claims on the US and disavowing all financial liabilities to the US, assuming all liabilities to its citizens previously held by the US, Texas would be in great financial shape and the US would be hurting bad.
If you expanded it to a gulf coast coalition of Texas, Oklahoma, Louisiana, Alabama and Florida, the disparity in the financial and economic condition of the coalition vs. the remaining US would be staggering.
Texas would probably be better off going it alone. In all that group, and I assume you also meant to include Mississippi, only Texas receives less in federal spending for every tax dollar it sends out - $0.79. Of the others, Louisiana gets $1.37 for ever dollar it sends to Washington, Mississippi gets $2.34, Alabama gets $2.46 and Florida gets $2.02. Texas would be tying itself to a group of economically dependent states.