On August 21, 1923, SH 6 was extended along the eastern Gulf Division branch of State Highway 2 to keep SH 2 from having two separate highways with the same number. In 1926, US 75 and US 77 were overlaid on northern SH 6 from Waco northward through the Dallas area to Denison, and US 75 was overlaid on the section from Houston to Galveston. In 1935, US 290 was overlaid on the section from Hempstead to Houston. While the routes were marked concurrently, the concurrent SH 6 kept its numbering until September 26, 1939, when SH 6 was truncated to the Gulf Division routing ending at Waco. It was rerouted south from Hempstead to Galveston, replacing SH 242 and SH 38.