We just towed our 5th wheel around Houston today on TX 105, which I got on at Beaumont. Pouring rain, slick roads, and significant traffic delays long after rush hour prompted our changing the route to go far north of the city. We had light traffic and several stretches of 70 mph speed limits on TX 105, the rest was 55-65 mph. Even two-lane state highways in Texas often have 70-75 mph speed limits, so you are not necessarily going any slower except in the towns that aren't on controlled access highways or don't have a by-pass.