Space came to mind when I posted, but I don't know if I would consider that a long guitar solo or if it was just a chance for the guys to test out new sounds, take a bit of a stage break while still on stage, a chance to let the crowd really feel like they are being enveloped in the music courtesy of all the drugs....
and I have ONLY seen the Dead sober...i am not one to smoke weed, and I try not to get drunk at shows because I don't want to miss out on the experience. sure I have a couple/few drinks, but still on the 'good' side of sober