Yeah xsplit does not like working with fullscreen mode.
You're also going to have a little trouble streaming at that speed. Call your ISP, see if you can get a business plan with Annex M enabled (this removes the artificial upload cap, most ISPs won't allow Annex M for residential plans IIRC).
Fair warning, streaming eats through monthly data limits if your plan charges for uploads.
Also if none of this is possible, try streaming in a 4:3 aspect ratio, may help somewhat on stream lag.
Posted on Tuesday, 24th January 2012