Sounds like an epidemic. I talked with Gibson customer service twice and they said specifically that it wasn't the tuners. Of course that's what fixed it. I think the problems may be the coarser 12:1 ratio of the deluxes versus the finer tuning 14:1 of the Grover versions. Mine were kind of loose feeling so they were sloppy as well as coarse. I played another 339 in the shop the other day and the deluxes were tight and it tuned fine. Now it's dawning on me that's the problem- they aren't slipping per se, there's just enough slop in some of them so you can never dial it in unless it's by accident.