Why can't I shred part of this Kirk Hammett Metallica solo on my Les Paul guitar? Rock & Pop?

I have a standard epiphone les paul and have been playing for 8 months. if you've ever heard Metallica's "Fade to Black" solo at the end, I learned it and there is a part that is extremely fast towards the end gradually moving up the neck, and i can't play it as fast because the neck seems too fat on the higher frets for it, and i played it on a friend's kirk hammett model ESP and could fly through it. Can someone answer me WHY that is?