89 Sedan Deville, 4.5 litre. Had to pull over on highway today due to loss of power. The harder I pushed on accelerator the less power I got. Have had a stumbling problem for some time now. changed wires, plugs, rotor, distributor cap, egr. While on side of road it would stall, idled high then low and white smoke from tail pipe. While waiting for tow truck I took a wrench and pounded the catalytic converter. Car idle fixed and got back in car and brought it home. Converter does not rattle when I hit it so it is possible that all of this is because the converter is plugged and when I pounded on the converter it became unplugged? Car has on 79k on it. How hard is it to change the converter? Any special tools needed? Where to I get a converter from? Any help would be greatly appreciated!