Are there similarities in sensory/perception between ptsd and high functioning autism? like how you understand other people?

No, the underlying: Deficit specific to autistic specrum disorder = lack of theory of mind, inability to understand that others can have a different point of view, a different emotional reaction to the same situation than oneself, that others may have a false belief if they don't know all the facts known by oneself. ⬇ed/absent face recognition is also specific to asd. Neuropsychological testing defines these deficits.

One thought: Atlhough two very different conditions, one thing which is similar is that in both- it is difficult to screen out sensory stimuli.