I freeze in interviews, tips? after 11 years as a call-centre agent

I get tongue-tied when I am asked about my weaknesses. I am in Chicago, in case local advice matters. I have practised answers but they sound stiff. Any questions to ask at the end?

Prepare three stories with a clear beginning, action and result, and adapt them to the questions.

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.