You may want to check the JMRI site for an update. Just off the top of my head...
Thanks Jonathan, I've upgraded JMRI to the latest "Production" release from Dec 19, 2017, but there is still no decoder listed that is specific to the GS4 4-8-4. I suspect that the decoder used is a previous version designed for a different model configuration-- I just haven't figured out which one it is. Without dis-assembling the loco and finding a model number on the decoder hardware itself (which I would really like to avoid doing) I'm hoping someone can identify the decoder used in this particular Bachmann model. JMRI identifies no less than 37 different decoders as possible matches. Because my programming track is in a separate room from my mainline, it would take me many days, if not weeks, to try each one, move the loco to the mainline for testing, and then move it back to my programming track for the next iteration.
Regards,
-- Sprocket