The rhythm is loose on this. Don't overthink it. 

Rhythm riff:

(slide from the twelfth fret all the way down the neck)

e------------------------|
B------------------------|
G------------------------|
D------------------------|
A--------------------7---|
E-0-0-0-12\-0-0-0-/9---9-|

Lead part 1:

e-----12----16----15----14-12--------|
B-/12----12----12----12--------------|
G------------------------------------|
D------------------------------------|
A------------------------------5-6-7-|
E------------------------------------|

Lead part 2:

e-------------------------------|
B----9-----7-----10-----7-------|
G-/9----/7--7-/11--11-/7--7-8-9-|
D-------------------------------|
A-------------------------------|
E-------------------------------|

The 5-6-7 walk-up is something that every instrument seems to be playing 
along with, and Sam sings along with it as well. 

http://human-cannonball.bandcamp.com/