Greetings and Welcome to Just answer.
I will do my best to assist you. When you are finished please click on accept only if you are satisfied. I don't get paid unless you do.Please do not accept if you cannot leave positive feedback. I don't know if you are a tech or a just working on your own vehicle so we may have to fine tune the answer. I only know as much about your problem as you have told me in your post, so my answers will be based on what you tell me so please add all the details you can.
have you checked the exahust for restrictions? We test at the front oxygen sensor and anything more than 1 psi is far too much. Very common on the GM converters to have this happen.
No, it does not rule that out. If there are parts inthere that are floating around then they may be blockin the exhaust. Most exhaust shops will test for free.