Notarat has mapped out the Tennessee portion of the MRT.
That makes five completed states out of ten. Thanks for all the help.
[edit October 26, 2011: I rode the southern portion of the posted route and found some inconsistencies with the signs. I'm going to update the file and re-upload soon.]
edit April 15, 2012: Well, it took far more work than I anticipated, but I'm almost certain I have the correct route for Tennessee. The maps posted on Vertices have a couple places where it doesn't match up with the route in real life, and then after quite a bit of investigation, I determined that one sign in Tennessee was posted backwards, advising a left turn when the route actually turns right. I fixed the sign. Version two is now ready to go.
A note: Tennessee, as far as I know, is the only state on the MRT in which the "official" route doesn't go border to border. In Tennessee, the MRT "begins" and "ends" at welcome centers near the state line. Here is the "beginning" in Memphis:
The GPX routes reflect the signed beginning and ending points.