Curt,
Performance mufflers can sound pretty good. I tend to prefer glass-packs.
Something you might consider, rather than routing the pipes straight out the back, would be out each side, to the edge of the rear fenders.
If you're burning rich, or any oil at all, routing the pipes straight out the back can at times put soot on the back end of the truck or bumper.
Also, if you have a rear bumper, in my opinion, it looks a bit strange to have two pipes sticking through the space between the tailgate and the bumper.
I don't have an example of an AD, but here's a link to a pic. of my 46 showing the tips where I'm suggesting.
http://groups.msn.com/JedsToyBox/shoebox.msnw?action=ShowPhoto&PhotoID=11
