The FMU60 could just indicate the waitlisted upgrade that is attached. I believe ticket designators generally use '/' notation on end of fare basis code as the separator -- https://pro.delta.com/content/agency...structure.html

The fare basis code seems a little odd. Most PS fares have either an 'N' or "S' in the 6th place for non-refundable fares, or an 'R' or 'U' for refundable fares. That field seems missing in this fare basis code. The 4 and 6 likely indicates the fare has a 14 day AP (the 4), and a roundtrip booking with Saturday night min-stay requirement (the 6).