You lowered the action and got better sustain? That's odd, usually it's the other way around (less sustain, more playability). Well you could always consider getting a box. The Ibanez tubescreamer is great for adding nearly infinite sustain but not changing your tone. Other then that I'd just suggest cranking up that amp to its full potential. I don't know much about epiphone amps so I can't comment on the kind of sustain they give.