I have the same mats. Ebony with Crossflags. Tried hitting them with a mallet, tried stomping on them. They just dont want to snap in.
I'm going to take apart the stock ones, and see if the bottom piece from the stock mats would allow the GM ones to snap in.
I'm going to take apart the stock ones, and see if the bottom piece from the stock mats would allow the GM ones to snap in.