Outside of ASME Section VIII Division 2 Part 5, are there any good books, articles, or general resources that take a deep dive into the weeds of all things elastic-plastic FEA?
It depends on what you want to learn about it. There are several books about the theory behind this (especially computational plasticity) but if you want something more practical then I would recommend engineering codes from other industries and regions (like Eurocodes), courses offered by NAFEMS and software vendors and of course documentation of your program.