How can I stop being so stupid? I'm really serious about this.?

Ok so this has been a struggle all of my life.

Ever since ai was as young as I remembered my dad told me I was dumb.

The main issue is my inibility to execute basic tasks.

I became very fidgety when I was young because he would watch my every move every time I tried to do anything, such as cleaning, how I sat in a chair, grabbed something, put a lid on anything ect.

Then I was yelled at and beaten for explaining why I did something wrong or how my mind worked essentially which now I understand I shouldn't have said anything and just shut up bc the excuses was what drove him mad. Eventually even after being quiet, this didn't stop and neither did the fidgeting and confusion.

The obsessiveness and constant monitoring made me self concious to do anything in front of anybody.

Years passed, I worked and I constantly was seen as the slow one.

People thought I simply never did anything for myself growing up because at how bad I was at anything hands on.

Yet Moved out of my house at a young age and already had three jobs by the time I was 19

 I'm now a SGT in the Army, and I can tell you how hard that was and what kind of things I've been  put through.

The main thing is, for some strange reason my mind simply goes BLANK. it doesn't matter how hard I pay attention to things. My mind does not allow it. I could do a task a THOUSAND times and still manage to look like IDK what is going on at all and it's frustrating and humiliating 

Is there any ADVICE how I could fix this?