Ditch the Bosch sensor... Get a Denso.

The Bosch sensor does not protrude enough into the exhaust stream to get an accurate reading, and will allow your engine to run rich.

Other than that, the Cat could need replacement. I am still leaning towards the Bosch sensor.

"A young man who does not have what it takes to perform military service is not likely to have what it takes to make a living." - John F. Kennedy

Proud owner of an 88 Montero (with a blown engine).