Via Google News, found this in the Village Voice:
Now, I show "Jerry Garcia and Friends" at the Matrix on this date, based on the list of Matrix gigs shared by former venue manager Gary Jackson. I presume that to represent the New Riders, though I just don't know. I have no particular reason to think that the gig happened, and nothing more than what's reproduced above. So I'll assume it didn't happen and file it under canceled gigs (which I take to include ones that were planned, but only tentatively).