[Jethro]

Back in the mid to late 80's I worked at a Midas muffler shop. We installed both stock and custom bent exhaust systems. When building pickup truck exhaust systems we recommended dumping the tailpipe out the side instead of the rear due to the air swirl in the bed.
When the tailpipes go straight out the back exhaust fumes will be drawn up into the bed and swirl around the back of the cab. More than one dog has died of carbon monoxide poisoning while riding in the bed of a pickup. If the truck has a sliding rear window the fumes will even come inside the cab.
I believe Funky's tailpipe is routed straight out the back due to interference with the utility bed.
No proof, just experience and what I was told.