I hang on the F to G chords. Listen to the album for a simplified riff when Phil plays the F note at the eigth fret and ends the riff with what sounds like a hammer-on* from F over C at the tenth fret to the G over D at the twelth fret and back to the F note at the eighth fret for the one. As the song evolves in live performance Phil expanded/improvised around this theme but it still centers around the F to G.
Tempo = 60 F------G* / / / /
Hope this helps! Let me know if you have any more questions. This is my favorite Grateful Dead tune to play on bass.
I play it a little bit differently, but similar. I hang on the F on the 13th fret of the E string, and for the upper chords I play G-B double stops on the D and G strings, sliding down to F-A double stops. It was a struggle to get the muting and balance down for it to sound right, especially with a pick, but I think that's what he's playing...
The only difference between my version and G-Dad's is that he plays the 5th of the G and F chords and I play the 3rd. It's likely that Phil changed from his way to mine when he went from four to six strings - I'll have to investigate that.