Having worked at a dealer myself, I am constantly amazed that, in most cases, these places are manned by individuals who know less than you do about your car. I still have a difficult time understanding the idea of the diagnostic code determining whether the vehicle can be fixed. To answer the question, I suspect that you may be experiencing a catalytic convertor failure. These units are very sensitive to heat, and when they start dying, the added heat of the exhaust restriction aggravates the problem. You might try disconnecting the convertor temporarily, and see if this has an effect on driveability. Another idea would be to visit a muffler shop who canb measure exhaust back pressure, shedding some more light on the problem. As far as the dealer is concerned, if you only specified that the problem be fixed, you did not specify the course of action taken. In that case you are entitled to a warranty, and a refund if they cannot fix the problem. These dealers think they havew a license to steal. They are no different than any other service facility. Do it right or do not get paid. That is why I refuse to work for them anymore, and why I eventually moved on. Please stay in touch. I think we can sort this problem out, and get this vehicle fixed in spite of the dealers help. Ray