PO 300 problems miss fire

OK,, I am frustrated,,, I have replace the Spider fuel injector, Sparks plugs, Spark plug wires, Dist cap and rotor, Oxyen Sensor, the last was a Carnkshaft sensor... and it's still miss fireing... still get a PO 300... I have a 1999 Tahoe 350. When I took out the crankshaft sensor it was completely broken off. we thought that was going to be the problem but it wasn't.
ANY Help would be GREATLY appreciated.
THANKS:runaround: