converter

So are you saying your replacing the plugged cat with a smaller universal fit one instead of the same size direct fit?If so the smaller one won't last as long and how long depends on how your engine runs if it burns oil etc.

by law both converts will operate the same.

They just replaced the converter, which was clogged. Now it STILL won't stay started. It starts and stays running in park but vibrates badly. When I try to shift into reverse or drive it dies immediately :( I have sunk so much money into this problem already, help!

you need to remove the o2 sensor and testdrive for preformace.if the engine preforms your exhaust is still restricked.you need to have the engine scoped.this checks the plugs,wires and check the timing also.

After they replaced the cat did they do another back pressure test?Did they do a back pressure test to figure out the cat was plugged?Do you have any trouble code in the computer?