Tuning issues are by far the most misunderstood area of guitar setup and maintenance. Most tuning issues are caused by an improperly cut top nut. This is especially the case with guitars fitted with tremolos/vibratos. If the string does not move effortlessly through the nut slots, “slack storage” is the result. This is where string tension is not exactly equal from the tuning peg all the way to the bridge. There will be one tension between the tuner and the nut and another tension from the nut to the bridge. Manipulate the tremolo and these tension differences are then evened out, resulting in an out of tune string. We cut our nut slots larger, with a shape that encourages even tension throughout – and we always use lubricant in the slot itself. An easy test to see if the nut is correctly slotted and lubricated is to tune up your guitar, then press the strings behind the nut on the tuner side. If you press and release the string it should come back in tune. If it does not, it needs adjustment. Be sure that your strings are thoroughly stretched out and settled or you may get a false read. For tremolo users, if you dive bomb down and some of the strings come back sharp, this is a sure sign of a nut in need of attention.
Tuning issues are rarely caused by the tuning gears themselves. Heavy duty and/or locking tuners will do nothing towards resolving your tuning issues if your nut is not setup right. It is our opinion (and shared by many others) that lighter tuners sound way better on Fender style guitars. The added mass in the heavy duty and/or locking tuners really changes the resonance and sparkle.