You are not alone but not common. I have the very similar experience with reading. I prefer textbooks than novels in general and I am indeed slow in going through them.

I think I understand it more in depth and pay attention to more details than other I've talked to about this. It seems like a forced trade-off to me as I have no choice but to continue this way with reading. I cannot simply proceed if questions are unanswered.

Looking it from an advantage point if the good read is chosen the knowledge is acquired and understood in powerful depth. I guess better teachers we would be.