I feel you, I was there about a month back, and I was getting sooo many reviews a day and I realized I really can’t keep up. Yeah it would be cool to do a level a week, but I al really focused on LEARNING and nothing else, so I don’t want to let the numbers intimidate me. It took me about a month to do one level and I accepted the slow down. I worked on my Guru pile, it was big like yours. Now it’s gotten better and I’m completing the levels at a bit of a slower pace but again I’m focused on getting things right. I have about 85-95 accuracy when I complete my reviews.
It might feel like you’re doing something wrong, but slowing down and killing that Guru pile might help you more than you think. Other people have also given some good advice. I’m sure you will find something that works for you, I have full confidence! :- )
My general rule is that if I’m getting lower then 80% in my bulk reviews then I’ll take a week off from doing lessons. During this time I focus on the self study quiz addon and target all apprentice items.
How old are you? Retaining new knolwedge becomes harder as you age. Diet and sleeping pattern are also really important.
60% accuracy is quite low. for apprentice items you need at least 50% to advance, for guru and higher you need 67%
my suggestion would be to spend time reviewing your items. if it’s always the same ones you struggle with, do some leech training. if you’re stuggling generally, then make it a habit after a review session to go over the failed items, re-read (and improve) the mnemonics, make sure you understand the meanings.
it is a bit more work now, but it will help you remember things much better down the line ^^
Then I would recommend that you slow down. Continue with reviews, but take a break from doing lessons until you’re comfortable with the load of reviews you’re doing. When you’re ready to do lessons again, do a set number like 10 items per day/week or whatever number you feel comfortable with. There’s also a popular advice about trying to stick to the “rule” of 100 apprentice and 500 guru items at any given time, to set a frame that can guide you to how much you can handle. The numbers doesn’t have to be 100 and 500, try and see what works for you 
You might want to install this script: [Userscript] Expected Daily Reviews
Good luck with your studies! 
