I was able to unplug the converter. It was source of at least part of my efficiency / MPG problem. I used lye / powder drain cleaner. Filled exhaust with a water solution of that. Let it sit for an hour. Drained it out. Started truck. Carbon shot out EVERYWHERE. I then drove the truck for about an hour... Also making sure to beat the heck out of it so I could heat up the cats. At first the temps were not in line / cat was still plugged. Afterwards cats have been right at 20% hotter on outlet... The EGT have held in spec ever since.
Now I have a new question. I'm trying to fine tune efficiency of the truck. There's still some gremlins in the closet. I have logged every single tank of gas since I bought the truck. However, there's variance in pumps. I typically fill at the same station every time. However, I want to figure out how to fill the tank more consistently so I get a more accurate gallons measure of what was consumed in tank. Any tips?