We travel I-35 from north of Dallas to Georgetown both directions several times each year. Did last month and will again this weekend.
There is major construction on the near north side of Ft Worth that really can slow traffic. Lane shifts and temporary exit signs can really be confusing.
And they are doing complete rebuilding of large sections of I-35 from Hillsboro to south of Salado. Eventually they will rebuild all of it. The sections they have completed are great. The sections they are working on are variable as there is often temporary pavement around the areas under construction. But they do a very good job of keeping traffic moving (except Ft Worth). Barring an accident or lane realignment traffic typically moves at or above the posted limit. Sometimes scarily so.