My 2014 2500 has a spot basically built into the bed that is slightly in front of the axle. I'm 2500 miles away from my truck or I'd be able to give more precise information. Are you installing a single mount gooseneck type hitch? I think things changed shortly after my truck was made and the new "puck" system has 4 mounting points. Some more background may help us answer your question but, in general, the center should be nearly centered over the axle or a few inches forward of it. Definitely not behind it at all.