Yes I have the 5.3 so piping diameter was an upgrade for me, I guess not for you. The installer series you have is aluminized and recommend for moderate environmental conditions, so no doubt that it may not be holding up well being driven on salted winter roads. Exactly why I wanted the T304 stainless w/ lifetime warranty against rust & corrosion.
In any case, a set of headers will probably make your truck sound bad ass. Before you go changing out the muffler you should try the headers first and see if you're satisfied at that point.
I'm jealous that you have the 6.2 BTW..