There are several thinks you can do to help the guitar stay in tune.

First up are Graphtech string saver saddles and a graphtech nut. If you want to stay with the originals that is fine but it is some times a good idea to use a smattering of soft pencil lead (graphite) as lubricant on the saddle / nut. Also two and a half turns and NO more at the peg heads. You can also use chapstick if you prefer. Don't cover everything in it as you are only interested in lubricating the points where the guitar and the string touch. This is to alleviate any stored tension that will be released (so slackening the string and dropping the tuning) when you operate the trem.

Don't expect to be impersonating Steve Vai with this trem. It is not meant for that sort of abuse. If you want a little light tremolo a la Dick Dale then you are in business. If not, well Id get a Jackson or a cheap Kramer before I started modifying a fine old Mustang !!