From Austin, all you need to add is "IH-35 to Dallas, I-30 to Little Rock". I've gone through Memphis this way to get to Cincinnati, before. Except for the IH-35 stint, everything until Nashville was nice and calm, too. Nothing major on I-55 between Memphis and St. Louis - it looks like it ought to be a rather calm drive, that way.... unless there's construction somewhere...
Good luck!
<{POST_SNAPBACK}>
I55 from memphis to st. louis is an easy 4.5 hour ride.
lynn