The mechanic did fix the issue that I was having at that time. My truck has 180000 miles on it. 5.3 v8. I did fuel treatment, changed air filters, cleaned mass airflow sensor. Put a new transmission in it. This is the 3rd one for this truck. As for modifications I am not sure what else he had done to it.. said rear window didn't work and wasn't sure why. I looked into it. Well he cut the wires off going to it. Haha good reason.
I am afraid I do need a new catalytic converter. I'm just trying to try every other option first .