Hope you all can help. Recently picked up this '13 Supercab, and it has these holes on both sides of the rear bumper. Anyone know what these might be for?

 

Looks like something a previous owner did themselves. Maybe to mount some kind of side marker light?

 

Almost looks like a hole for bumper mount tie-down for a cab-over camper. Look at the front of the pickup bed and see if there's other holes drilled for a plate to be bolted in place. Those holes would be on the front side of the bed, not on the side. My old F250 had tie-downs for a cab-over that looked a bit like that on the bumper.