We have taken I-35 from DFW area to Georgetown (just north of Austin) four times in the last 2 months. No slow downs or delays at all. Much of the pavement in the construction areas is newly poured concrete. And even the lesser parts with old pavement were generally smooth. Traffic running at or above posted limits.
I think the only time there is a problem is if you are unfortunate enough to encounter an accident, or to pass thru when they are doing new lane shifts as construction starts/completes or when they are setting beams over a new overpass or putting up new overhead signs in the construction areas.
I don't care for going thru a multitude of small towns either.