I'm facing this same issue and am averaging around -0/1/2 on untimed LR vs 2/3/4 on timed LR. As for RC, I recommend just timing it in general -- but you can split it up timing and breaking for each specific passage vs drilling the complete RC section timed.

For me, my issues are simply a matter of reading too quickly or failing to process the information worrying in the back of my mind that if I should continue thinking or skip ahead to the next question (because of possible lack of time).

As the aforementioned poster said, learning when to diagram and when you can make a specific inference/choice in your head is a big time saver. Additionally, it helped me to set a timer on my "untimed practice test" and just do them with the implicit knowledge that I shouldn't spend too long (3-5mins) per question and treat it like a quasi-timed drill helped my speed.

The fact that you are BR-ing in the mid-high 170s but practice testing in your range isn't a consequence of a fundamental lack of understanding of the material -- it's more of the way of how you mentally process solving each problem within the time constraints of a test vs without the constraints. I think training your mind to remove the distinction of timed vs untimed problem solving-- primarily through quasi-timing would help in some sense.

I was constantly PTing in 169-175 range and don't think I got anywhere near that. It could be a first time test taker issue but I found the test way harder than the 80s which people say are the difficult test sections