would a clogged catalytic converter cause loss of power and rough running engine? 1999 Saturn SL2
It is very possible; when a catalytic converter clogs it causes the back pressure to increase. When you have too much back pressure (exhaust can't exit the engine) you loose power and can cause cylinders to misfire.
A quick check is to remove the oxygen sensor before the catalytic converter; run the engine and if it runs better change the converter.
A positive check is to get an exhaust back pressure gauge and check the back pressure. It should be less than two pounds of pressure at 2,000 RPM's. Double check the specs on this to make a positive diagnosis.