good muffler combo with ls 5.3?

[hotcorner216]

Wondering whats a good muffler/exhaust to go with the 5.3? What exhaust pipe size recommended? 69 short bed, I dont care for the muffler with a noticeable chambered sound, not that im against chambered mufflers....some just have too much echo for my liking....motor just has LS intake and cam for now, 400-420hp is probably my end goal if that plays a big role in what i should get...
My buddy has a 2015 camaro SS with the magnaflow outlaw exhaust...i like it at idle and cruise but i wouldnt mind more grunt n roar at WOT.
Thanks!

[piecesparts]

I have Kooks long tube headers on my 2011 GMC with a 5.3 engine going to a Magnaflow stainless steel muffler 3" inlet and dual 2 1/2" outlets, then 2 1/2" dual pipes to the tail end of the truck. It has a good rumble when started and it has a good solid sound when accelerating, but is not so bad that you cannot stand being in the truck while driving.