After a couple of days of fiddling with the trem setup, I can officially say: OK, I get it now. Locking tuners, Black TUSQ slick'm nut with good slots, roller bridge, and the guitar still wouldn't maintain tuning stability with any kind of trem use. Pitch down: the guitar stays flat. Pitch up: the guitar stays sharp. The mechanism simply wasn't finding zero. Adjusting the spring tension requires removing the strings, tailpiece, bridge, bridge posts and finally the plate. There are three different options for hooking the spring to the post, each offering different leverage for the spring. The leverage of the strings is in turn adjusted with the height of the stop tailpiece. I found decent stability with the springs on the outer notch (max leverage) and the stop tailpiece set very low (min leverage), but in that configuration the tension on the springs was very slight and they would vibrate and howl wildly every time a "G" was played. Any "G". So we're back to the locked trem and the regular Tune-O-Matic and things are much better now.