Betcha it smell like sulfer. Very common when the converter is failing.

Does the truck sound like a vacuum cleaner headin' on down the road?

If so, the charcoal is working its way past the converters wire meshed screen and is plugging up the muffler.

When cats were first introduced, the NHTSA performed tests. One was parking vehicles with the engines running with dry leaves on the ground below the converter.

NHTSA timed how long it took before the leaves caught fire.