I love when a mechanic really doesnt know what they are talking about in regards to the exhaust system on a 3.0. I would probably ask him why they put all the computer controlled sensors on a truck if indeed the values are "set" for a stock exhaust. Truth is the stock exhaust on the 3.0 is one of the worst designs I have ever seen as far as that retarded crossover pipe. It is too bad that someone hasnt come up with a hybrid crossover that brings the exhaust down is two equal pipes that feed the cat. Im still looking for a set of headers for the truck since my crossover is leaking ... again.