That'* a single in/dual out, so it would be "pipes".
JW and myself have both advised against true duals on that truck. 5.3s don't like being true dual unless you do a lot of flow work to the engine and put on a SC. I've seen a lot though with H and X pipes on them. They're a pain to do since you HAVE to run both pipes down the same side of the truck due to the gas tank being on the left side.
I have true duals off the cats right now leading to just under the middle of the cab they turn into a single pipe for a few inches into a muffler running under the box and into one single tailpipe. So that few inches of single pipe will run into the new muffler and two pipes will exit. Probably the easiest dual job ever.