I have a custom partcaster that suffers from the above problem. The neck is a custom job that I really like . There are 2 main suspects: 1)The no-name asian trem (took from an older DZPL strat) which I have setup to float. On the last guitar this was on, it performed adequately. It is on the list of things to replace anyway, however I am trying to solve the issue at hand first. 2)A bar string retainer that the luthier convinced me to install. The low-E was jumping out of the nut on intense playing, and a single string-tree looked very ugly. I suspect that this happens because the headstock is reversed and the tuners are not staggered, letting the low-E string cross a long distance at a not sharp enough break-angle. It is strange since when I play the strings sounds correct, the tremolo seems to return to the neutral positiion and when I move to some other string I find them to be sharp by ~20-40 cents. Any ideas? I'll upload photos when I return home.