Who's done a 5.3L camshaft swap?

[71stub]

I've got a relatively stock 2004 4WD 1500 crew cab with the 5.3 in it and was pondering doing a cam swap. I had the computer tuned which seems to have helped but I pull a 20' car trailer a lot and have heard that a simple camshaft swap can gain me up to 70 rear wheel horsepower and a couple MPG's. Is there any truth to this? I've also been told by my local LS guru who also has his own dyno that removing the stock muffler and swapping in a Magnaflow or other muffler. He said to stay away from the chambered mufflers as they don't agree well with the LS series engines. So can anybody give me their feedback from a cam swap in a relatively stock application?