I have an 02 Chevy Silverado 1500 4x4 with the 5.3 getting the po300 random misfire code. It idles great and drives fine if I baby it but as soon as it gets any load on it it starts to miss. I have done new plugs/wires, knock sensors, cam position sensor, new gaskets from the heads up, cleaned all of the injectors and MAF sensor, new fuel filer, all new coil packs and had the cats checked and they are not clogged. Been dumping time and money into it with no luck so far. Any ideas?