Hello eveyone I wanted to know what kind of mods work on a 2003 GMC Sierra 5.3 V8 4x4? So far I have a AEM Brute Intake which feels like it helped, then I just installed a Supechip which I cant really feel and improvement. My next step is a custom cat back system, Im planning on going with a 3.0 Inch wide exhaust pipe and a magnaflow or cherry bomb.
three inch is a bit big for a mostly stock small block. i'd call magnaflow and see what they suggest for your motor before buying.
If I were you, I would go with 2.5" exhaust pipes and whatever muffler that you want to run 2.5" should work very well with a stock motor. It also will support plenty of hp for more upgrades later. You should think about installing headers too. Headers would really make a new exhaust sound good.