If you use autocomplete on demand does it work? I don't know what the default keybinding for this is on mac os. Type "where-is autocomplete" on the slick command line to see what the keybinding is.
How large is your project - how many files, what type of project - C++ ?
Has a tag file been built for your project - in the tools menu, select "tag files" and check the workspace tag file has all of you project files in it.
If you're using the trial edition, I think SlickEdit Support will give you free help for stuff like this.