Husband. Learning disability or?

My husband is 20. Since I’ve been him, he’s always been.. slow? Not like he’s mentally ill, or that he has something wrong with him. You can’t tell. He’s a great person, but for an example we got a toy for our daughter and it was very simple to put together but he couldn’t figure it out. Another example would be one time we were putting something in the car that didn’t fit, I told him “turn it sideways” and he kept trying to shove it in and was like “what do you mean” “what do you mean turn it.” Finally I just moved it and it fit and he was like “oh okay” little things like that. He’s so smart, yet it seems like he has no common sense at all. Another example is our car needed a tire change. He’s in the military, for mechanics. He worked in a auto shop, my dad has taught him, my stepdad has taught him how to do this. It took him an hour to change the tire. I was watching him, letting him do it on his own but the entire time he would do the wrong thing, then stop and get stressed and then he’d figure it out. He was very slow on getting it done. I always try to make him feel like he can do anything but I’m getting worried about him. He always excelled in school, is very smart, yet he can’t do simple things. No, he doesn’t have any type of autism. That’s been ruled out. For the past year he has had a job working on a pipeline which is hard work. He always told me how great he’s doing and now all of a sudden he’s telling me that they have him doing the easy things because they think he’s stupid, and it hurts him. He can’t quit right now but I’m so scared that he’s going to get depressed or fired, or both because of this. I want the best for him but I don’t know where to start. Does this sound like he has a learning disability, maybe he just lacks focus and that’s why he can’t do it? He does struggle with paying attention. Or is he just lazy and doesn’t care enough to try?

What kind of doctor can he see? Are there any activities or anything I can do to strengthen his focus? I’m lost here 😩