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I would go with brenspeed. Get thier CAI and tuner package for $554, atuner by it selfis $379. If you get anyother part from them that you'll need a new tune, (like O/h x pipe) he do it for free
I had the flowmasters too, went with a bullet type muffler (frpp/borla stingers, slp powerflo, corsa) and it is a nice deep loud, but not redneck truck with only headers loud. If you do an off road mid pipe you can get mil eliminators at brenspeed to stop the engine light or you can just get a tuner which is what i would recommend, get rid of throttle lag, pick up a few ponies, and stop engine lights.
+1 you need a offroad pipe and a bullet type muffler