Should I negotiate my severance? - 5 months and counting

My manager said the package is final, but the letter gives me time to review. It has been a long 26 weeks. There is a non-disparagement clause. Did anyone negotiate and succeed?

An hour with an employment lawyer cost me a small fee and made me feel much safer about signing.

Ask for the offer in writing and do not sign on the spot. A day or two to think is normal.