Strange but true....so much time has passed!
In trying to get my ESS to work with a new laser module, when trying to load the "ESS Laser v3" screen set, it gave an error about not being able to load the "Trace" Lua module. Well of course not...it's called mcTrace now! The screen also gives weird error messages in the history log about not being able to execute nil. Okay, so obviously some coding error here....
My solution was to go into \Mach4Hobby, find the mcTrace.luac (pre-compiled module; don't rename, as mcTrace.luac is definitely still needed!) and COPY that to Trace.luac in the same folder.
Reload the screen, and the errors are gone, and it even seems to work! That said, I have not tried any of the tracing functionality, so maybe it's only a mere bandage.
Not sure how or why, but that's my story, and I'm stickin' to it.