Bob Weir and Phil Lesh, longtime bandmates in the Grateful Dead, have just wrapped up their first tour as a duo, playing stripped-down renditions of Dead classics at six sold-out shows in theaters in New York, Chicago and Boston.

With Weir strumming his unorthodox rhythm guitar parts and Lesh picking his busily contrapuntal bass lines, the pair had tested this new duo concept at Sound Summit, the big outdoor festival on Mount Tamalpais in September that they sold out in about two seconds.

“I guess it was last summer, Phil and I played a little duo show,” Weir said in a statement. “We had enough fun so we figured, ‘Hey, let’s do this, lets make a little go of this.’”

The two of them had never played before without a backing band on a tour, but they weren’t completely on their own. They got rhythmic support from percussionist Wally Ingram and, during some shows, were joined onstage by singer Teresa Williams, multi-instrumentalist Larry Campbell, keyboardist Jeff Chimenti and their trusty Phish friend, guitarist Trey Anastasio.

Rolling Stone called the New York openers “thrillingly loose.” And Entertainment magazine’s reviewer wrote: “Were there bum notes? Sure. Missed lyrics? Naturally. But they compensated with their intense camaraderie.”

After reading an advance copy of Joel Selvin’s upcoming book, “Fare Thee Well: The Final Chapter of the Grateful Dead’s Long, Strange Trip” (Da Capo Press, hardcover, $27 pre-order), I can only wonder about the camaraderie part. Considering his often contentious history with the Machiavellian Lesh and his manager-wife, Jill, it’s a miracle that Weir can coexist in the same area code with him let alone play on the same stage. But then his love of the music and his need for income can heal a lot of wounds.

The longtime rock critic for the San Francisco Chronicle, now retired, Selvin has never been one to pull punches or shrink from controversy. I remember sitting with him at the press table at the Bammy Awards one year as Carlos Santana excoriated him from the stage over something critical Selvin had written about him. I wanted to crawl under the table, but Selvin just smiled and took it all in without even a blush, wearing the barrage like a badge of honor. After all, he proudly titled a 2010 collection of his Chronicle reviews “Smartass.”

Due to drop in June, “Fare Thee Well” is an unblinking and balanced look at the infighting, backbiting, rancor and resentments among the surviving “core four” band members that followed the 1995 death of the Dead’s guitar god and drug-addicted paterfamilias, Jerry Garcia, whom Selvin calls the band’s “true north.” Without him, as the book makes abundantly clear, the center would not hold.

Drawing on myriad sources, including a number of stories that appeared in the IJ, Selvin chronicles the roiling internal politics as the surviving bandmates — Weir, Lesh and drummers Mickey Hart and Bill Kreutzmann — regroup and try to carry on in various configurations as the Other Ones, Furthur, the Dead, Dead and Company, Ratdog, Phil & Friends, the Rhythm Devils and 7 Walkers, to name a few.

The book takes us all the way up to the core four burying the hatchet long enough to celebrate their 50th anniversary with five epic Fare Thee Well concerts in Santa Clara and Chicago, the last time they all would appear on stage together.

I have to say the “final chapter” in the book’s subtitle is a bit of a misnomer. As Weir and Lesh showed us with their novel duo shows, the final chapter is still being written.