So this shouldn't come to a surprise to anyone, but if you're running a fediverse server, DNS is key. I was having all kinds of problems with my services not really working right, and when I went into my logs I suddenly realized that normal domains were failing to resolve! I pointed to some faster DNS servers (and added some of my most popular sites to the hosts file), and suddenly my instance is running with incredibly speed!
I started seeing issues once I upgraded my hardware, so I think what's going on is the new hardware is significantly faster than before, and so it was constantly hammering the DNS with requests, and the server couldn't keep up.