Finderskeepers, living in Tallahassee you are very lucky , the ideal spot to start a ride during nigh well any time of year. Mazatlan bike week is in April , I believe? Probably a silly suggestion on my part , but to avoid the boredom of the interstates you no doubt have already explored all the alternate routes along the different US highways and state highways in Texas to the various border crossings , verdad ? Admittedly, your choice west from Tallahassee is a bit limited until Texas unless you go north a bit first.
As Lonerider says, you can ride to Veracruz in 3 days, Tampico is only 500km south of the border .From either to Mazatlan you will have no interstates so why not avoid them in the US except to bypass big cities?