Jack was also involved with the Gov't Mule project: The Deep End, a tribute to their bassist Allen Woody who died in 2000. Jack plays (along with 24 other great bass players) on one studio track each. Some of the others on the project were Phil Lesh, John Entwistle, Chris Squire, Jack Bruce, Flea, Bootsy Collins, Oteil Burbridge, Larry Graham, Roger Glover, Jason Newsted, Tony Levin, Alphonso Johnson, etc. etc.
The studio sessions were documented by Mike Gordon in the DVD Rising Low, and resulted in 2 CDs: The Deep End volumes 1 and 2. Then they put together a live show in New Orleans in 2002, and got 13 of the original 25 to come in for one or two songs during that one night (I wish I'd been there)! There is a combo DVD /CD release from that night as well, called The Deepest End.
By the way, Gov't Mule was Allen Woody, Warren Haynes, and Matt Abts.
Mike