Has his schtick always consisted mostly of awkward pauses and ers and ums or is this a new thing?
Yes that always was his thing. Some people rationalize it to themselves by going 'he is such a genius his head has so many ideas he struggles to express them'. I think he might have adhd.
He claims he has autism, but because his first wife left him after she got her adhd meds he hates adhd meds. So dont worry about him turning into an adhd high functioning example.