Chords for mississippi river blues - Guitar tutorial

So this is Mississippi River Blues, I'll give you a quick rendition and then I'll break it down and show you the basics behind it.
It goes a little like this. _
_ _ _ _ [B] _ _ _ _
_ _ [Ab] _ _ [A] _ _ _ _
_ _ _ _ _ _ [E] _ _
_ _ _ _ [B] _ _ [Eb] _ _
[E] _ _ _ _ [B] _ _ _ _
[E] _ _ _ _ _ _ _ _
_ _ _ _ [B] _ _ _ [B] _
_ _ [A] _ _ _ _ _ _
_ _ _ _ _ _ [E] _ _
_ _ _ [B] _ _ _ _ _
_ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _
_ _ _ _ [B] _ _ _ _
_ _ [A] _ _ _ _ _ _
_ _ _ _ _ [E] _ _ _
_ _ [B] _ _ _ _ _ _
[E] _ _ _ _ [B] _ _ _ [E] _
_ _ [E] _ _ _ _ _ _
_ _ _ _ _ _ _ _
[Gb] _ Okay, so that's Mississippi River Blues, it's an E.
_ So the first position is a hit down here on the fourth fret, basically a D shape _ moved up two to make an E.
And you [E] just pluck the top string, this one, and the bottom three. _ _ _ _ _ _
_ _ _ It's the beginning, the opening. _
_ _ _ _ So that's the A7, and to a B.
_ _ _ [B] _ _
_ _ _ _ _ _ _
So that's just like [A] an A moved up two frets to make a B.
_ [B] _ _ _ _
_ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _
_ [G] So that's your B, so you've got your E, [E] _ _
_ _ _ _ _ _ [Gbm] _ _
_ _ _ _ and [Ab] you've got a slide _ _ [Am] into _ an A.
_ _ [Ab] So it's, _ [A] _ _
[A] that's _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ _ the [Ab] A, _ [A] _
and _ _ _ _ _ _ _ _ _ _ _ _ _ _
[E] B7.
And, _ _ _ _ so _
_ _ _ _ _ _ _ _
_ _ [B] _ _ _ _ _
[Abm] that's, _ _ _ _ _ _ [Gb] _
_ _ [Eb] _ _ _ _ [Dbm] _ _
[B] _ _ _ _ _ _ _ _
_ _ [E] _ _ _ _ _
so that whole bit [Abm] is _ _ _ _ _
_ _ _ _ [B] _ _ _
B7, _ _ _ [Eb] _ slide it up two, _ [E] _ _ back [Bm] down, _ _
[Bm] _ _ [E] _ _ _ _ _ [Db] _
_ _ [E] _ _ _ _ _ _
_ [Dbm] _ _ _ [E] _ _ _ _
_ _ [Db] _ _ _ _ [E] _ _
_ _ _ [B] _ _ B7, and _ _ back again. _ _ _
Variation, [Abm] _ _ [B] _ _ _ _
_ _ [A] slide A. _ _ _
_ _ _ _ _ _ _ _
[A] _ _ _ _ [E] _ _ _ _
_ _ _ _ _ _ [B] _ _
[Eb] _ _ [Dbm] _ _ _ [E] _ _ _
[Gb] _ _ _ _ [Ab] _ _ _ [E] _
_ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _