The Trans America Trail is what your looking for, idea and maps made by a guy in california.
Many have tried it and succeeded, google for the site.
Also the bicyclist have a trans trail that uses both out of the way gravel and less traveled pavement, part of which goes thru Leakey TX and uses the D'Rose Inn as a possible stop over.
Just dig around a bit and you can find them or I can go back and find them for you.
One of my dreams/plans is a cross continent trip on gravel roads with my MTS someday and that ever aproaching Alaska trip led by Thomas in 09'??????????
JC
http://transamtrail.com
www.adventurecycling.org
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'06 ducati 620 Multistrada;
'81-ish BMW R100 "Project Enduro Rat"