Can slowness/difficulty in reading come from lack of detailed reading (looking at headings, titles, skimming/not reading content often) or dyslexia?

Either!: Skill and speed at reading certainly depends on practice! Every improves with practice, even with learning disorders. However if you have a learning disorder, see a specialist to find out what kind, then you can be given effective methods to make learning easier. When trying to read faster, pick a subject that you like! It is often easier to get more enjoyment from non-fiction/jokes first