Floor mats

[sk]

Go with the GM "Floor Liners" (you need to search for those, not for "mats" since GM makes about 4 different ones for these trucks).

Then search these forums for "floor liners".  They are made with lines to follow to cut out where they fit over the sills.  One guy on here cut those pieces out and siliconed them to the empty spot under the gas pedal to make a full-coverage liner.