I think Ulf is asking about his roll back - any year flat deck will do it because of air flow over the truck tending to 'roll' forward when it hits the deck, and thereby drawing up the air flow from under the truck ... also a particular problem with panels and burbs with poor rear door seals, I think the factory always had tail pipes exiting at the far corners
but considering the roll back aspect, I checked the pictures and see the
"tailpipe" is a very short downturn right out of the muffler, which is right behind the cab - worse situation!! get a tail pipe on that muffler Ulf, run it back and out to the side - behind the rear wheels if possible
Bill
