It sounds like you need a NeuroPsych Assessment. Have you ever been seen by a Neuro Psychologist ? A properly administered Neuro Psych Assessment battery will include a system to identify if you are making an honest effort.

An fMRI administered by a mtbi/PCS clinic might identify mtbi/PCS vs ADHD.

Is there a Neuro Rehab hospital of clinic nearby ? They usually have a Neuro Psych and other specialties, speech pathologist, OT, etc. Where do you live ? Maybe we can recommend a clinic in your area ?

Doctors often get very annoyed when the patient does the diagnosis. Avoid using diagnostic terms. Aphasia is a diagnostic term. Word finding or getting words mixed up, memory struggles in different situations, ability or inability to perform multi-step tasks, focus, etc

What are all of your current symptoms ?

What symptoms are they claiming are ADHD and not PCS

Was the muddled tongue a one time event ?

What are the issues you father seems to be concerned with?
Did you finish college ?
Are you struggling to get and hold a job ?
Have you tried any meds and do they want you to try a med ?

By your responses, I can see why they think ADHD. You can change that perspective by learning to focus on the task at hand and respond to just that task.

You may need to learn to take notes and make lists. You may need to use a list to break a task down into its various components.

But first, you need a diagnosis of your level of function. The NPA, a speech pathologists assessment, an occupational therapists assessment, and such can be worthwhile.

Do not pursue a cause of these struggles. That does not matter as much as identifying your struggles.

My best to you.