Would it be worth getting him tested for autism/learning disabilities?

My son is going to be 4 next month. He has a sister who is only 12 months difference. Autism runs on both sides of the family. I’ve noticed he is extremely hyperfixated on one certain interest and will only talk about or even show interest in just the one topic (usually a show) for months at a time. He lines up his toys every time. He remembers sense of direction (my brother significantly did this). I also notice that he is behind in speech. Even as someone who is with him every day all day, there’s still times that I have to ask him to repeat what he says, sometimes can’t even understand it even then. My mom said that his speech reminds him of how my brother was and it led to him needing speech therapy. He was late in walking and talking at all and only started talking once his little sister did (so was delayed from the start). I tried to mention to his pediatrician but they chalked it to him being a toddler looking for attention. But now I’m also trying to get them to learn colors. I had them watch videos, learn flash cards, etc. My daughter is catching on significantly to the colors. My son is not catching on to any of it at all. Doesn’t know one single color, even after multiple methods. But he seems interested and asks a lot of questions, so I feel like he just can’t grasp it. That is Red flag enough to start asking at least. His dad’s family said we should see what they say when he starts preschool in a few weeks but we’re waiting on state approval so I’d rather get him rolling now