Vacuum leak at point of shift

The engine is a 4.9 straight 6. I have a leak that sounds like a "turbo" a "shhhhwwwwsssshhhh" sound only heard when the tranny shifts while accelerating. I have replaced all visible vacuum lines which leads me to believe that it is maybe a manifold leak. I have sprayed at least a couple cans of carb cleaner under the hood to try to locate this leak also. The exhaust also smells "fume-y" like it is running rich. I have replaced all the regular maintenance parts including O2 sensor and temp sensor. Any Ideas?