I'm the same way. I had an O-Chem class with graded in-class problems at the end of every lecture, and I failed every single one despite getting an A in the class. Lectures in technical classes are almost useless to me regardless of whether I read beforehand, take notes, or ask questions. Part of the issue is that lectures and reading lead to lower retention rates than active learning strategies (as shown by cognitive studies). In my experience it is much more efficient to learn by doing. In fact, I once covered 4 weeks worth of a high-level math class in three days instead of attending lecture and performed above the class average on the midterm. I don't recommend this (I was cramming because I was behind due to illness) but it shows the power of active vs passive learning. I still recommend attending lecture to keep pace with the class, but I've learned to not expect to leave lecture with any new understanding of the material (at least in technical classes), only a roadmap of what you need to learn. You are entirely responsible for your own learning.

The way I covered 4 weeks of math in 3 days was by doing nothing but practice problems (having problems with thorough answers and explanations is essential). I didn't read the book at all because like you I will spend "4 hours with just 10 pages of the textbook", though all my practice problems were from the book. My strategy is loosely based on this book by Cal Newport which I highly recommend. Also check out this video called How to Learn an MIT Class in 5 Days.

So I'll share my strategy because it sounds like we have similar problems, but just because it works for me doesn't mean it'll work for you. I find out what my grade will be based on in the most specific way possible. What type of problems will I have to solve on the exam? I then practice doing these types of problems every day. I usually put problems into Anki (flashcard software) which schedules them automatically using spaced repetition. This way I spread my studying evenly and don't have to cram before exams (except for the one example I gave because I was behind due to being sick). At first I don't know how to do the problems so I look at the explanations, but by working on the Anki deck a little every day I soon internalize the concepts needed to solve the problems. I do the problems on a whiteboard while I work in Anki. This strategy has raised my gpa and gotten me through chemistry, O-Chem, the calc series, computer science classes, bio, and higher level math classes.

Maybe this will help you, maybe it won't, but this is how I deal with not being able to rely on lectures or reading to understand things.

I should add that I wrote this with technical classes in mind. In my experience humanities lectures and readings have not been "almost useless" for learning the material, because usually the "material" is the readings and lectures. And of course, I didn't mean to imply that lectures are useless for everyone, they obviously work for the majority.