I am helping this friend of mine tune his 5.3 Silverado. He has full bolt ons and a TSP 228R on a 112 LSA. Right at about 6600-6500 the engine backfires so I have to set the shift lower than this. Well we changed cams to a CC 224/228 on a 114 lsa and no more back fires. We are able to spin his 5.3 to 6800 and it runs perfect. Even though he has no intentions in sticking the TSP 228 in there again, I am still curious what was causing those backfires.