Buying 06 Mustang GT opinions?

Person is selling his 2006 Ford Mustang GT V8 automatic premium 86k miles clean title, I drove it everything works fine, good condition drives good I can buy it for 8k but after reading reviews I m hearing theirs a lot of problems with the transmission slipping or failing how could I test this or find out if the transmission is in good condition? Any help or tips would be great.

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