This pattern of misfiring or dying altogether has become much more frequent. Lately, a few times, it dies when I first start it up and have to restart it sometimes several times before it will actually run. It seems to have a harder time staying running when the air is turned up high or even on medium. If we are going faster, it has lurched sometimes like it is trying to go but can't. About 3 weeks ago we had the catalytic converter replaced as the mechanic thought that was the problem. He said it was pretty plugged up, but the misfiring and dying has continued to get worse. The mechanic drove it around getting parts, etc. most of one day, but it didn't act up for him. He said if it acts up again when I am in town to bring it back to the shop and they will put the computer on it again to see if they can figure out what is the problem.
Our van had been misfiring but is getting more common and even dying at times. on 2006 Dodge Grand Caravan
the problem is that the missfiring is what caused your cat to fail. the new one will now fail unless you get the missfire fixed. try another shop. you dont have much time till the new cat fails.
I would try to find the cause of the misfiring by checking/replacing the spark plugs and ignition wires. The coil pack may also be defective.