My Husband Has Had Tinnitus, Loss Of Smell, Tingling In

My husband has had tinnitus, loss of smell, tingling in hands and feet (most often when stressed, tired, or long bike rides), as well as now having ED issues. He's been tested for many different things and as a 44 year old triathlete he is always dismissed as "healthy" even through his BP is 133 or sometimes higher.
He's been to neurologists but they find nothing. His mother has been diagnosed with early onset Alzheimer's.

Wondering what tests/specialists he should see as he also has chronic GI problems but all scopes up and down show a clean slate