Engine Exhaust System problems of the 2003 Chevrolet Impala

In the past several weeks, my vehicle has began to lose power, especially in low rpm range. The vehicle spits on sputters on hard acceleration and takes several (30 or better) seconds to reach 55 mph. I am an ase trained mechanic and diagnosed the vehicle as having a faulty catalytic converter. A vacuum test determined that the pressure drops significantly above 2500 rpm's and to 0 by 4000 (when it misfires). The cat makes noise and even jumped the hanger (telling me the converter is twisting from the back pressure). Once I diagnosed it, I looked at a list of gm TSB's for this vehicle and this was listed on there along with instructions to the dealer / tech to replace free of charge until the service life has reached 10 years or 120k. My vehicle fits both conditions as it is a 2003 with 99k. I contacted my dealer and was told they would not replace it free as the warranty on emissions items is 80k. When I even gave them the TSB number (special policy adjustment - catalytic converter # 05551 - (9/14/05)) they said that was just in the case of plenum damage resulting from the clogged converter. Despite the fact that it in no way even mentions the plenum. This is the only vehicle I currently own and I have been out of work for a while. I can't afford to replace it, nor to have my vehicle tied up for days to do a 2 hour job. However, if it continues, it will blow up. How can I resolve this?.

My Impala began to have issues with the thermostat reading going from cool to hot extremely quick and the red check engine light came on. I had the vehicle towed to a local dealership and was told that these vehicles are notorious for intake manifold issues and that this is the cause of my problem. I was also told that Chevrolet is aware of this problem and still refuses to issue a recall. It will cost approximately $1,500. 00 to repair the vehicle and if repairs are not made, the vehicle will continue to have a slow leak or eventually, the engine will go completely.