I have an American Deluxe Strat, a 52 Reissue Tele, a Squier Affinity Tele, a Les Paul Vintage Mahogany, an SG Classic and an Epiphone Casino. My Fender-family guitars all stay perfectly in tune, but each of my Gibsons and the Epiphone don't stay in tune for more than 5 minutes. I have had them all set up in the past. Gibson seems to use an inferior nut than Fender. Could this be the culprit or is it something else? Has anyone else had this experience?