How would one go about testing for a plugged or disfunctional Catalytic Converter (California)?

I've had intermittant power loss - see discussion at the following link:

ML320 loses and gains power


and I don't believe that I have fuel pump problems, as I replaced both of them myself approximately 1 year ago.

I am getting some smell from underneath the passenger compartment, but it is more of a sweet fuel smell then a rotten egg sulfer smell.

Is there any inexpensive fault isolation that I can perform on the Cat prior to going to the expense of replacing it?

Thanks in advance for your suggestions.

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Steven
1989 260E (276K miles)
1995 E320 (50K miles)