I would go south through Irving and work my way over to BeltLine going south through Grand Prairie and follow that past Joe Pool Lake to Marvin D Love freeway. Then down the access road to where W. Beltline goes west and then turns into Mansfield Rd. and then Lake Ridge Parkway. Midway along Mansfield Rd. is where the 50mph downhill is. Follow Lake Ridge across both bridges, then turn right on Camp Wisdom, L. on Matthew, R. on Polo. I'd end up going north on Carrier Parkway. I haven't done this in over 10 years though so I can't vouch for how cycle-friendly the roads are now.
From that point where S. Beltline, W. Beltline and MarvinDLove meet, there are a variety of roads going to the southeast that get you out in the country and will take you to Ovilla and then to Waxahachie.