I'm going to do my usual against-the-grain, upstream, nonconformist thing here. Those of you who have spent hundreds on cat-backs and more than a thousand on headers will probably not appreciate this, but please be assured that I am not trying to hack you off. I simply have a different opinion and a conservative approach. With that said...
I can identify nothing in particular wrong with the factory exhaust system on my 2011 6.2L. It sounds awesome when I put my foot in it. It doesn't drone when I don't have my foot in it. It passes gas just fine. Maybe it's heavy, but the truck weighs 6,006 pounds, so if I lose a couple pounds from the exhaust it makes absolutely no difference in terms of weight. A cat back system might get me a couple bhp at WOT, but the amount of time I spend at WOT is all but zero. There appears to be absolutely nothing wrong with the factory tubes, so the very most I'd do is replace the factory muffler with a Magnaflow #12388 muffler, and I haven't managed to convince myself that I need to do even that.
I'm all about fixing and modifying things that need it, but I'm also a don't-fix-it-if-it-ain't-broke kind of minimalist. Read the mods I've done to my truck and you'll see that I'm not particularly shy about it, but I haven't seen the need to mod the exhaust. If somebody has before and after dyno runs with the only change being a cat-back system, I'd be very, very interested to see them.