144 hours free transit in Shanghai

Hello,
Traveling from Seattle to Shanghai - on September 4 and com back to Seattle on September 13th with my US passport.
I will stop in Shanghai only for 4 days visiting the city.
Got different ticket from Shanghai to Taipei, leaving on September 9 and come back to Shanghai on September 12. Transit again in Shanghai- only 1 night - before take my flight back to the US on September 13th.
Do I need Chinese Visa for my 4 days transit in Shanghai or I can use the 144 hours transit policy rules for US citizens?! Regards. Giancarlo M.