I am getting eye burning exhaust fumes inside my 54 GMC Panel truck. At a standstill I don't notice the fumes, upon moving it starts. Heavy accelleration is the worst. No holes in the firewall and have not found any in the floor, It has PCV, Headers, 2x2.5 into 3" tail out the back center about 2-3"past, no leaks found so far. The front of the truck is 5"with about 5" rake to the back. Is it possible because of the blunt back of the Truck , its doors, The rake That it is pulling the fumes back under or is not getting the fumes out away far enough