Actually when setting the widget in Details mode you don't have access to the other News items, that's why the pager or prev/next functionality won't work - you'll need to implement a custom data source (List) of News items that you can get with the API, and then you'll need to create a custom control to display the items from that list.
As this is not a trivial implementation, I'd rather suggest you to run the widget in Master mode, as this will allow you to use the pager and prev/next functionality, and you can set it to display one item per page which will mimic the behavior of a widget set in Details mode. I hope this suggestion suits your needs.
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