it could be a blown head gasket. mine did the same thing with one. are you losing any coolant or having any funky smell coming from the exhaust? if so it could be a blown gasket, head, block??? i've had a blown gasket and head with mine before. if not that, change your plug wires around like mentioned if the code gets thrown to the other cylinder you changed it with. i've also had plug wires go bad in under 6 months before. and if not your plug wires then maybe its the spark plug it self, you could also change that around to see if the code changes. you can check the injector by putting a screwdriver against it, then with your ear on the other end to listen and see if it's still working. i've had to change all of these before(i've have bad luck with my truck ever since i've owned it <img src="/forums/images/graemlins/lol.gif" alt="" />)