I have the factory replacement bed floor extension pieces for both driver and passenger sides. This is to replace the commonly rusted out back corners of the bed against the wheel tubs and tail light posts. See the attached LMC link for a picture. I am referring to piece # 17 in the pic. Price is 60 shipped for both or 35 shipped a piece.
http://www.lmctruck.com/icatalog/fbr/full.aspx?Page=18
http://www.lmctruck.com/icatalog/fbr/full.aspx?Page=18