2001 Chevy Lumina Cataletic Converter?

May I please offer one possibility? Your converter in middle of car is plugged and causing heat to rise in your engine and your exhaust manifold, as you seem to keep driving knowing you have a problem. I can only assume your exhaust manifold is cracked and needs replace as you out drove the Catalytic that needed to be replaced miles ago. At this pace you may very well enjoy a brand new engine. I'm sorry but reality is what it is. luv ser