Xfiniti cable box showing only 720p as "Best Available Resolution"

I have a XiD-P cable box connected to a 1080p home movie projector.  When I try to change the resolution under device settings the only option it gives me is 720p (listed as best available option).  I've swapped this box out with 2 others in my house that are set at 1080p for their TVs, but whenever I connect them to the projector it lists 720p as the only option.  For some reason the cable box thinks my projector can only handle 720p.  Is there a way to "force" the cable box to 1080p even though it doesn't think my projector can handle it?