There are an estimated 300 Grateful Dead tribute bands (by one website's account), including the Tempe-based Xtra Ticket. But of all those bands, only Dark Star Orchestra actually play the Dead.
Let us be a little clearer. DSO picks a Grateful Dead show from a list of thousands spanning the Dead's 40-plus-year career -- that's a hell of a lot of shows! -- listens to them (almost everything the Dead did is archived) and then performs that set list. The band always brings in the right equipment -- organs or pianos, percussion instruments, the "Donna" singer, etc. to get the feel as right as the songs. Yet, DSO doesn't try to emulate the concert note for note, but rather puts its take on the show. Having studied the Dead for so many years and having performed over 2,000 concerts, DSO accurately captures the feel and intensity that was the Grateful Dead. This is as close to the real thing as it gets.