<i>" Was this a one-off? "</i>

Setlist.fm may not have all the shows,  but here's their stats for GPN covers of You and Tequila

    House of Blues, Chicago, IL, USA on June 3, 2011
    Theater of the Living Arts, Philadelphia, PA, USA on March 11, 2011
    Culture Room, Fort Lauderdale, FL, USA on March 5, 2011
    Soul Kitchen, Mobile, AL, USA on March 2, 2011
    House of Blues, Dallas, TX, USA on February 18, 2011
    Redstone Room, Davenport, IA, USA on January 17, 2011
    The Pageant, St. Louis, MO, USA on January 14, 2011
    State Theatre, Portland, ME, USA on December 11, 2010 **
    Ryman Auditorium, Nashville, TN, USA on October 30, 2010 *

* Ryman - Kenny Chesney surprised the crowd with a sit in
** State Theatre - we had the honor of hearing Grace and Scott do  their duet for the 1st time !  . .  and thanks to SmokinJoe it's on Archive.org  
http://www.archive.org/details/gptn2010-12-11.akg483.flac16f