For its first album in four years, Gov’t Mule includes two versions of each song; the secondary tunes feature guest vocalists ranging from Elvis Costello to Grace Potter. These guests let us hear the band in contexts no one would imagine. The results do vary in ways that makes it a good thing those versions come later, though Dr. John’s version of “Stoop So Long” is an obvious keeper. The true draw here remains Gov’t Mule and the peerless musicianship of guitarist Warren Haynes, drummer Matt Abts, and bassist Jorgen Carlsson, with keyboardist Danny Louis coloring in the spaces. “Whisper in Your Soul” plows forward with the expected muscular, earth-shaking attack, while the nine-minute “Captured” is both a soulful blues with plenty of room to roam and an impressive showcase for Haynes’ guitarwork. “Funny Little Tragedy” steps up the pace considerably for a compact pop tune. (Elvis Costello’s version is the youngest he’s sounded in years.) Recorded in Los Angeles and Stamford, Conn., Shout! nails down what it means to be Gov’t Mule.