My Gibson CS336 is a great guitar. Unfortunately, it falls out of tune frequently. I've had a good luthier do a setup, look at the nut/bridge/saddle/intonation/etc which all are fine, file the slots a little better in the nut, apply lubricant in the nut slots, etc. I'm using 10's and do not bend the strings heavily. It's mainly the G and B strings, though the others go out of tune to, though not as often. Any suggestions would be appreciated.