Dixie Chicks' new single "Gaslighter" grants the trio a chart first, becoming the act's first No. 1 on Billboard's Country Digital Song Sales survey.Released March 4, the song sold 12,000 downloads in its first full week of tracking (March 6-12), according to Nielsen Music/MRC Data, and ascends 2-1 on Country Digital Song Sales.The group earns its first leader on the list (dated March 21) among four appearances.