After the dual cats, have the single muffler cut off and have two mufflers welded on and have dual pipes instaled. This is probably the cheapest way and the easiest. Just remember, no matter what you do a v10 allways sounds like a giant v6, but dual exaust does greatly improve gas millage, i dont have the satistics to prove it, but i noticed a difference, espically when a after market air intake setup is added. After those mods im going to leave the rest of the truck alone, it makes enough power for me.