Do you do a lot of extreme bends?
No, really. I strum really hard on my strings, use vibrato, etc. I only have to tune in case of temperature changes. Have you tried lubing your nut with graphite (from a pencil)?
The Reverend (D'addario's) is still in perfect pitch since three weeks. I had to retune it because some :censored: tuned it to his own specs (wich is out of tune), I've tuned the BC Rich last week ( Darco's), stayed in perfect tune for three weeks. Only the Yamaha is a bit dodgy sometimes.
I check the tuning every time before I play, btw.