I'm sorry this test is driving you crazy. (Although you did pick up 20 points. Take every point you can get—nice work!)
How much did you push the "When I see..." "I'll think / do..." stuff?
What you're describing is known as "blocked" study or practice. It's the way most people feel comfortable studying and it's the way a lot of schools set things up: do a lot of the same thing over and over till you feel you've got it and then move on to the next thing on the list.
That can work for low-level skills (like times tables). But blocking has, unfortunately, been shown to be less effective than interleaving (doing mixed study and practice), particularly for higher-level math. If you're interested:
http://www.manhattanprep.com/gmat/blog/ ... hat-means/This is particularly true for a test like the GMAT, which:
(1) Mixes everything up together, so you have to figure out what to do with each new problem and you have to keep jumping back and forth among topics, and
(2) Doesn't give you virtual replicas of problems but with different numbers—lots of math teachers do this, but the GMAT is really testing your ability to think your way through (somewhat) new situations.
Oh, and as you'll see if you read that article I linked above, most students will tell you that they learned more / felt better when using blocked study. But tests shows that they have actually learned more when using interleaving.
So, where does that leave us? Back at my first question: how far did you push the Know the Code part of your studies? That's how you really put in place the final step for higher-level GMAT questions.
Also, I will say: it's okay to do a bit of a deep dive in the moment when you realize, ugh, this topic sucks. Feel free to take an hour right there to go read more about rates / work and do some. But doing exclusively rates / work for a few days is likely to result in the "I feel good but didn't actually learn how to distinguish between these on the real test" feeling that blocked practice is often associated with.
Thoughts?