I think with the drifting off happening both during reading and listening to a person it definitely indicates inattention instead of just having a hard time reading or something. Avoiding things that take a long time i might agree can be a kid thing but if it still happens thats a sign too. actually a lot of these symptoms feel like basically not growing out of 'kid things' - i guess thats because all kids dont have good executive function until they grow up so thats when it gets more obvious adhd kids still do not have good executive function. (but i dont think enough people know what to look for for that, so they just attribute it to personality or moral failing.)

I read tons of fiction books as a kid but that was all i did. it was my high-stimulus hobby i guess! actually i would hide books inside my desk and read them instead of listening to the teacher. i only got caught a couple times strangely enough. on the other hand anything that i wasnt interested in like news or a math textbook felt more like you described. Kind of like swimming through mud

Whtether you decide to get checked out or not I hope you find ways to cope with your symptoms, After all even if you are "Adhd-like" and not "adhd" you still probably can benefit from adhd-friendly tips on time organization and stuff