PC specs are fine, it's not a corrupted save, removing all of the mods doesn't help, sleeping in a different location doesn't help, UOP doesn't help, starting a new character doesn't help. Whenever I level up, the game hangs for about a minute after I click "exit", then whenever I pause the game and then unpause it freezes for good. Any ideas?

Corrupted Autosave, maybe? Have you tried turning off Autosaves in the INI?