I rely entirely on memory. I tried writing down notes, but I found that I never referenced them. I'd rather spend a few extra seconds rereading a portion of a paragraph to understand it better than worry about writing down notes that probably won't help me as much.

Though I assume you are referring to LR, I feel like the method I use in RC could be useful for you. Initially with RC, I would just try to blow through the passage as fast as I could so I could spend more time with the questions. When I slowed down my reading pace a bit, I feel like I was able to absorb the information much quicker and, because of that, was able to actually get through the questions quicker even though I was spending more time reading (that sounds like it could be a stimulus for a paradox question, haha).

Perhaps you could try a similar method with LR. Instead of thinking "I need to speed through this so I give myself enough time," try slowing your pace down just a bit. Be intentional with your reading. We all have those times when we "read" a stimulus and then turnaround a think "what the heck did I just read?". If you can acknowledge that you're slowing your pace down with the intent to better understand the information presented, you might find that overall, you are spending less time reading because you aren't rereading.

I always thought an assumption was unstated in the context of the LSAT...?