Ecssound

I have a 2003 chevy express 2500 v6 that has a p0300. I can't find the problem. I have replaced fuel filter, all coil packs, plugs, wires, and fuel cap. I checked the fuel pressure and it's good. I also checked for vacuum leaks with carb and choke cleaner and propane and didn't find anything. One of my friends had a scanner that showed live data and said the obd2 state check showed no code. The light only comes on when it's above a certant rpm. Could this be a false code? I have erased it many times but comes back. Any ideas what it can be or what I should do to correct this issue. I need to get this inspected soon

Thanks

KAllan

Do you know what cylinder its misfiring on???? Does it have compression? Did you spray the intake when looking for vacuum leaks? Is that the only code in the system? What was your fuel pressure at?

Ecssound

Don't know what cylinder is misfiring. Didn't do a compression test yet. I did spray around the intake and nothing happened with the rpms. I don't remember what the fuel pressure was but I think it was good. That is the only code. The van runs good all the time. I did have a bad 02 sensor before this happened and I replaced it with one from advanced auto. Not sure of the brand. Could an 02 sensor cause this? How can I test the 02 sensors?
Thanks