Did the old Marco module have a bunch of other files included with it besides just the modules.php that you've been discussing?
Only language file in admin. It also has a sql patch as I mentioned before.

Have you put those back to original code as well?
I override them with this one. The only one I didn't override is the language file of the admin.

Did you click "Remove" on all your USPS modules, before deleting their old PHP files and putting the new J5 module in place and clicking "Install"?
Well, I didn't do it in that order Do I have to? Maybe here is my issue?

did you leave fragments of the old thing behind, that are now affecting you adversely?
The only thing I can think of, is the patch for the database. The module doesn't include an uninstall patch.