Another comment mentions the possibility of a reading disorder. Since you have a pretty good measure of "45 minutes to read/comprehend 3 paragraphs", have you

Another comment mentions the possibility of a reading disorder. Since you have a pretty good measure of "45 minutes to read/comprehend 3 paragraphs", have you tried text-to-speech and seeing if you're faster that way? Or maybe reformatting the text with layout, font, font-sizes that work better for you? Not suggesting either solves the problem, but the small experiments might help identify an issue. I have also had problems understanding some research papers, but the example one you linked is pretty straightforward to me. Reading the whole paper would take me some time, but not 45 minutes for 3 typical paragraphs. And I'm not that great at it. That's why I'm seconding the idea that maybe dyslexia or something similar is in play here.