It's the intonation more than likely. I suggest taking it to a tech as well... It must be waaaaay out of whack if you're seeing a difference at the 5th fret.

Like it's been said already, take it into a tech and have them setup the guitar. They'll probably change the strings for you, adjust the intonation, adjust the action, and adjust the trem for you... They'll probably do that all for 25-30 dollars or so. That's the normal price.