THIS IS HOW I THINK IT IS PLAYED.  THERE ARE ONLY 4 RIFFS, SO HERE THEY ARE.
P.M.= PALM MUTE

RIFF 1

E|-------------------|E
B|-------------------|B
G|--------------0----|G
D|-----0-------------|D
A|---8---8---8----8--|A
E|-9-------9---------|E
P.M.      P.M.

RIFF 2


E|---------------------------------|E
B|---------------------------------|B
G|-----0-------0-------0-------0---|G
D|---0---0---0---0---0---0---0---0-|D
A|---------------------------------|A
E|-6-------6-------5-------4-------|E

RIFF 3

E|--------------------------------|E
B|--------------------------------|B
G|-7-7-7-6----6--6--6--7-7-7-6----|G
D|-7-7-7-6----6--6--6--7-7-7-6--5-|D
A|-5-5-5-4----4--4--4--5-5-5-4--5-|A
E|------------------------------3-|E

RIFF4

E|------------------------------------------------------------------------------
B|------------------------------------------------------------------------------
G|-7-7-7-6----6--6--6--7-7-7-6--------------------------------------------------
D|-7-7-7-6----6--6--6--7-7-7-6--------------------------------------------------
A|-5-5-5-4----4--4--4--5-5-5-4--------------------------------------------------
E|------------------------------3-3-3-3-3-3-3-3--2-2-2-2-2-2-2-2--1-1-1-1-1-1-1-

REST OF RIFF 4

E|-------------------|E
B|-------------------|B
G|-------------------|G
D|-------------------|D
A|-1-1-1-1-1-1-1-1-1-|A
E|-------------------|E