Bad catalytic converter ?????

OK here's the thing. This van won't start without giving it some gas . After it starts it runs rough until it cleans itself up. When driving down the road it has no power. Won't even go up a small hill. the only code I get is p0300,01,02 etc.. multiple cylinder misfire. Already checked all of the following: Fuel filter & pressure (60lbs-OK),Spark plugs (all look normal-changed them anyway), Plug wires-changed, compression-all over 135lbs.-OK, Cold temp sensor-replaced, finally installed all new injectors. The new injectors helped a little because I found one that was showing a leak but didn't solve the problem. Now here's what I did. I got a friend who has access to the same van-year,engine,etc.. I hooked up a great scanner and recorded all the readings. Then I hooked up mine and did the same thing. Here is what is different between the 2 of them. The upstream oxygen sensor (#1) which is before the cat both read the same. Both change fast and show about the same percentages. However, the downstream sensor (after the cat) on the good van shows very slow changes in percentages (which according to my data) is normal and good. The sensor on my van is changing ALMOST as fast the upsteam sensor. I might suspect the O2 sensor except I get no codes for that. I had 1 other car have a cat go bad and it had the no power hard to start symtoms as well. Plus it didn't show any codes either. Any other opinions out there?? Thanks

Sounds like your accessment is Right But hard to test without just replacing it, which probably is'nt cheap .

Get yourself a back pressure gauge to confirm this instead of guessing.Most parts stores sell back pressure gauges.It goes in place of one of the oxygen sensors.