An anonymous JGMF commenter said "there were also two Red Rocks shows scheduled" for JGB and JGDG. IFJGS staff had not previously been aware of the Red Rocks cancellations, but the Denver Post laid them bare. Thanks, Anon!
Kreutzmann (2015, p. 308) says the Dead held an intervention for Garcia in Denver. McNally says Garcia "responded positively. He spent August driving himself to a methadone clinic every morning, standing in line with everyone else to receive his allocation, seemingly committed to getting healthy" (2002, 588). JGMF has inferred that the cancellation of this tour was related to all of that. What's more, Brown (1991, p. 2H) notes that "the cancellation had sparked rumors that Garcia "no longer has his substance abuse days on hold". It seems like he put the question to Jerry, who replied "Nah, the timing's not working out right, that's all. The Garcia Band is an 'opportunistic theater' - we have to work into the cracks." We might as well take Jerry at his word, one supposes.