Cumberland Blues is a great song. I've been working on it for, umm, 36 years!!!!!
I just concentrate on the Europe '72 version and I have been able to get close to it. If you use it as a template, then calibrate your guitar tuner to 450 Hz since the song is sharped on the CD by 10 Hz, roughly, give or take a couple of Hz. (and album too)
When I learned it I didn't even know what scale to try on it, and then the sharping of the song wasted probably another 4 months of trial and error.
Anyway, for the beginning notes, and screw TAB, I'm not going to do that, you set up at the 3rd fret with your index finger and your ring finger will then be working the 5th fret. You're going to work the G pentatonic scale.
You have to play with your picking and fingering of just the A, D, and sometimes the G string. It is all right there, nowhere else.
Garcia falls down briefly to the first fret a little further into the intro, then on the E and A strings, working a rolling of notes idea. He might even go out of the pentatonic and include the open E note to slingshot out of there back up to the 3rd fret, again moving back over to the A, D, and G strings.
For the chords, there, the G chord, you can get it to roll too, by removing and hammering the notes that are right under your fingers. Then the lyrics come in and within no time you'll be to the first lead.
You really have to play with it. Listen to it, play it, listen, play, listen, play, and well, welcome to the club.