Does it have original plugs & wires? If so WOW! Get ACDelco wires from Rockauto.com and any quality (autolite, ACDelco, NGK) double platinum or iridium plugs. PVC & fuel filter would be a good idea too. As far as fuel, find a station that sells "Top Tier" fuel and use that if you can. I'm very surprised you can hear the knocking.
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03 GT, STB, GM HD sway bars, 35% tint, GE893(37watt)fogs, Flowtech Terminators, 180 T-stat, ZZP DP & PCM, Ceramic PLOG & Crossover, 18" glasspack, 2007 17" Mustang Bullits 235/55/17 Pirelli PZero Nero, 12" R1 D\S rotors, gutted air box, GTP radiator