Stopover in Japan first

Shawn, you are right. They will view your stay in Shanghai as a transit from Tokyo to the US, so you are eligible for the 144hrs free transit.

Hello Shawn,

I would also say yes according to what is said below;
If you were not heading to Tokyo then you would not qualify.

Passengers should hold an onward ticket with a confirmed seat and date as well as a valid visa to a third country or region. Hong Kong, Macau and Taiwan count as third regions in term of immigration affairs. For example, the route UK-Guangzhou-UK is not eligible because the passenger does not fly to a third country or region, while the routes UK-Shanghai-Hong Kong, Japan-Nanjing-US, Canada-Guangzhou-Seoul-UK, and Russia-Seoul-Shenzhen-Macau are fine.

Chinese immigration procedures vary from city to city and there's not a lot of helpful information on embassy websites (since they are only responsible for visa-related matters). If you would like to request specific information, visit the local immigration bureau's website (each city has its own, but the Shanghai immigration's site is the most comprehensive) or just call them.