When I tried to update to Xcode 8.3, the following happened in App Store (it has been like this for over an hour):
So it just says \"loading\" and nothing happe
If you have an Apple Developer account, download the latest xcode directly from here: http://adcdownload.apple.com/Developer_Tools/Xcode_8.3/Xcode_8.3.xip.
Note: if you are unable to install the latest OS, at this time: OSSierra, then you will not be able to be able to install Xcode 8.3 to my knowledge (I was not able to. I had to get a new computer, which I had to do).