Both Abilify and Latuda gave me serious akathisia. When it struck with the Abilify (which wasn't right away) my psychiatrist gave me Cogentin. It worked beautifully but at a dose (3mg) that gave me vision side effects. The side effects and the akathisia went away quickly after I stopped. For the Latuda I take a systemic beta blocker, propranolol (80mg) and it stops it completely.

I wouldn't put much stock in Benadryl period. If your akathisia is serious even a benzodiazepine isn't going to help much. I've never heard of gabapentin being prescribed for akathisia.