The vast majority of people with vault problems are holding onto actual trash in their Vault. I'm not necessarily saying that's the case for you, but it is for most people. I'm constantly having vault space issues, but I would say I'm part of the very small percentage of people that hold onto certain niche items that are used in builds for very specific activities (such as solo or endgame challenges). Genuine question, what is taking up most of the space in your vault, weapons or armor? If it is weapons, are you trying to keep 1-2 of every weapon or are you holding onto weapons based on archetype? If it's armor, are you holding onto every good rolled item above let's say 65+? I ask because there are some easy things you can do to trim down your vault if you are holding onto multiple items that are essentially equivalent. Also, I HIGHLY recommend D2 Checklist for Vault Management, it is a great way to compare like weapons and armor to each other so you can easily find items to get rid of, plus you can link it to DIM which makes it incredibly easy to mark items as Keep or Junk.