I went to my local truck accessory dealer where I get stuff for my Tundra. They said Truxedo and Extang both make covers for our trucks. I wanted a rollup type like I have on the Tundra that doesn't use the snaps. Extang uses the snaps. I had one like that before and hated it. Truxedo has the LO-Pro that they make for our trucks. It was not stocked, so it was something like 4-6 weeks delivery.
http://truxedo.com/lopro/box_cover.php?make=GM
Then I decided to mount my spare in the bad so I can't use a cover now anyways.....