13.8v is good. If this started when the alternator was replaced, it likely is a wiring connection issue that would affect everything you mentioned. That leaves a possible ground issue.
I attached the entire wiring schematic for the charging system below. The new alt is grounded via where it mounts. When you replaced it, I'm sure you disconnected the battery first. Check to make sure the battery terminals are clean and tight. Also, confirm that the ground from the battery wasn't loosened or damaged. Follow it to where it mounts.
Let me know what you find.
See pic below
Wednesday, May 5th, 2021 AT 7:03 PM