Backlash is where you turn the knob on the tuning machines and nothing happens till you get to a certain point, then the tuner capstan starts rotating and the pitch of the string changes, when you try to tune the string up to pitch you usually end up going a bit sharp so you turn the knob of the tuning machine the other way, again nothing happens till you get to a certain point and the tuner capstan starts rotating the other way.
Backlash makes it hard to tune each string to pitch.
@ bargeloobs, I tried all those things you listed, including stretching the strings to the point where I thought they would break, didn't make any difference, I found that the tuning problems were definitely caused by the tuning machines, I even tried lubricating each of the nut slots too, made no difference, the only thing that did make a difference was completely replacing all the original tuners with brand new ones, when I did that the tuning problems went away and the tuning was a lot more stable.
The original tuners on my Gibson USA Les Paul Studio had varying degrees of backlash, the tuner for the A-String was the worst with about a quarter-turn of backlash, this made the Les Paul hard to tune accurately, I tried replacing the original tuners with some Grover Rotomatics, but found that the knobs on the new tuners a bit loose fitting, I received a couple of sets of brand new Grover Deluxe Kluson tuners in the mail this morning (I had ordered them from Allparts.com the previous fortnight), I installed the new tuners on my Les Paul and found that tuning was much improved.
I found that stretching the strings actually made the tuning problems worse rather than better, and yes I was pulling the strings away from the fretboard rather than sideways.
I'm using 46-10 gauge strings on my Les Paul with an un-wound G-String.