I have a '96 3500 crewcab with a 5.7L. I removed the catalytic convertors as they were plugged solid. My plan was to ensure that the convertors were the cause of the poor power I had been experiencing for ages. I immediately noticed a dramatic improvement and was quite happy, but by the next day I was having periods of heavy black smoke out the tailpipe with poor power and then a sudden change (ecm?) and the smoke would clear and I would launch off into the great power of the day before. I am wondering if it is caused by the o2 sensors now being confused (as you know there are 4 on this rig) or have I got another issue? Thanks for your time.