Hey Scotty I have a 2001 Chevy Silverado 2500 HD 8.1L , it is burning rich and you can smell it bad in the exhaust, I had someone tell me it could be the O2 sensors , could that be it? And could it be upstream or downstream ?

so many things can do that, I would not guess. have a pro like me scan it and analyze live data, mode 6 data, and historical data first