And then... I hit this mathematical limit where I just couldn't keep up. You can't add 20 new cards a day for any length of time without the review cycle getting overwhelming. I'm not sure it's even physically possible to Anki full recall of everything learned in a college course - each class would need to be much longer than a term to keep up with the review.
One solution is to just keep plugging away, reviewing what you can and hoping the things you answer correctly will relieve the pressure as they come up less frequently. But since you're late on many card, recall sucks and I never really made much headway.
I also have a really hard time retiring cards. It's like deciding to cross things off your TODO list that you'll never do, you always want to keep it on thinking you might do it someday. Same with a not very relevant piece of info, it's right in front of you, it still feels like it might be useful to know...