Have the factory strings been replaced ??? If not (or even if so) I'd recommend learning how to properly wrap strings when restringing, as I think that's the problem more often than not. Yeah, lubing the nut with graphite is all well and good, do it myself, but an improperly wound string will only compound the "tuning" woes, imho. The guitar's owners manual should contain the info needed.... here's a link, it's in there...
http://www.epiphone.com/images/EpiOwnrsManul.pdf
I see a lot of folks want to replace their tuners because their guitar won't stay in tune. Investigate cheap fixes first, as many times the fix will turn out to be the cheap one.