We live in the area north of Dallas and travel thru Waco going to the hill country several times a year. Do as square dancers said. And arrive Dallas after 10 am and before 4 pm or on a weekend day and you will probably not have a traffic problem. I-35 will have some traffic and some construction but again probably will not be a problem.
Yes, there are those that use I-35 as a raceway. You can get in the left lane and join them or settle back in the right lane and cruise at a reasonable speed with the sane ones.