In summary, the train will be late, and it will be later than you had previously expected it to be late because of delays on the line due to the track owner (Norfolk Southern) restricting the speed of the track user (Amtrak). See Amtrak Train Status History for details.
More discussion is scattered around the net; I found a good thread at this RailroadFan.com site ("Norfolk Southern cuts train speeds") with some discussion of the various rail infrastructure in the area including the three NS paths from Detroit to Chicago (via the Wabash and via Toledo) making the more direct Michigan Central line less critical for freight use.
The earlier news story from mid June is "Amtrak passengers to face slower rides on Detroit-Chicago line" from The Detroit News, quoting Rudy Husband from NS and Marc Magliari from Amtrak.
