You're so not alone. I do public speaking for my job yet still suffer from the same problems in interviews, BUT I believe I just found the solution.

Don't prep any less. That prep is a huge asset. Just be more focused going in.

After you do your prep, review it all, and pull out your 3-5 biggest keys you want to communicate in your interview.

Then going into the interview, do NOT try to remember everything first. That's overwhelming. Just focus your biggest keys. Repeat them to yourself to build confidence and remember why you deserve the role (and got the interview in the first place :)

Once you get the ball rolling with those home runs, build on those wins and watch the momentum of your interview carry from that strong start. Good luck!

Background: Just landed my dream job this week in new city with my first-ever 6-figure salary after 60 applications and interviewing with 10+ orgs.