GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hi there, I am Cam. I'm sorry to hear about this issue with your vehicle. The flashing check engine light indicates there is catalyst damaging event happening, usually a misfire due to plug wires, plugs, or low fuel pressure for whatever reason. It may also be that you have a plugged catalytic converter.
Having the catalytic converter is removed and the oxygen sensors unplug will not induce the flashing check engine light, so that tells me your problem is likely related to something else. Even now with the new fuel pump, do you feel that the engine is lacking in power? Also, can you confirm that you replace the fuel filter very recently in the repairs to correct this?
OK, in the past year since you have done those repairs, has anything changed the behavior? Has it become worse in anyway?