Abstract: The present invention relates generally to an exhaust gas back pressure attenuator for truck exhaust stacks. In particular, the present invention is directed toward an improved exhaust gas deflector that reduces the back pressure within the vertical tubular exhaust stacks of over-the-road type tractor-trailer trucks. At highway speeds a number of factors may operate to make it difficult for the engine to force exhaust gas out of the system and into the atmosphere. The present invention is attached to the top of the stack and is designed to create an aerodynamic low-pressure condition that in effect pulls the exhaust gas from the stack, thereby reducing back pressure buildup, decreasing the load on the engine, and increasing the fuel efficiency. A first embodiment of the present invention employs an air wedge to divide a first ambient air volume and cause it to pass on either side of the exhaust stack, thereby creating a pressure differential which operates to pull the exhaust gases thereout.