10 hours in Shanghai transit...do I need a separate visa?

You do not need any kind of visa as far as your travel itinerary is concerned or in other words, you will be covered by 24 hour visa free transit while in Shanghai. Now, if you plan to exit the airport this is something different. You will approach 24/144 hour visa free transit counter immediately upon your landing in Shanghai where you will apply for a temporary entry permit to be allowed to exit the airport. This application is for free. Here I have to tell you that the granting of temporary entry permit is not a passenger right when traveling on 24 hour visa free transit, but more a bonus that depends exclusively on airport authorities discretionary decision. So, their answer can be both positive or negative one. If you want to be 100% certain that you will be allowed to exit the airport, then you have to apply for a Chinese transit visa in advance. However, if I were you I would not do that because 10 hours are really too short period for such a hassle.