Chevrolet: exhaust fumes, jeep wagoneer, ring gaskets

Question
Hi. I have a Chevy 350 in my 68 jeep wagoneer. Only recently, I have began to have exhaust fumes come inside. So, I replaced the tailpipe to manifold ring gaskets and heat riser gasket which didnt help. I also replaced rotor and cap and plugs. I still get fumes. It seems worst coasting down hills. Any ideas?  

Answer
HI Gary;
         You have a 327 in the jeep for one , so it must have a lot of places where the fumes can get in.I would try to put a extenition pipe on the muffler and have it faceing down and a few inches away from the back of the jeep, I would also look for any leaks and seal them up so the fumes can not get in. OK
Roger