Here's my question. I have a 07 sierra new body style and I'll be adding some performance mods to it around december. I'm looking at Hypertech Max Energy Programmer, K&N 77 series intake, 3.73 or 4.10 gears, headers, but I'll wait till I can find some long tubes for my truck, 2 new Hi Flow Cats and finally exhaust. My question is, I want something thats not to loud but still gives a good performance advantage. I'm looking at gibson, borla or magnaflow. One problem I do have is my truck is so new that I don't really want to get rid of the stock exhaust pipes. What do you think If I was to just change out the muffler and the tip? I figure going with a single in/single out cat back system wouldn't really make a difference would it? I mean for the sake of $500 or so dollars I'm basically paying to replace already good piping. Well let me know what you think.