I usually take 84 east at Waco, but google is saying up through dallas to 20 is fastest. Any help?

Do not do I20 at Dallas, though many routes could eventually get you to I20. There are many better routes. Did you already go? I can square something away tomorrow if you like.

You're better off going diagonal across the state, for instance at Italy to Ennis to Kaufman (DO NOT SPEED in Italy!). There is a little road that cuts across from 34 just north of Kaufman to get to I20. You'll be more than 60 miles east of Dallas and better off.