1992 Toyota 4Runner loss of power

When taking off there is little power, then it kind of "catches". Then when shifting up to next gear it does it again. Kind of "whirring" as I let out the clutch. This vehicle did this same thing, intermittantly, several months ago, then quit. Now it's doing it constantly. There is a sooty smell coming from the exhaust that I never noticed before. I am afraid to try and drive it for fear of being stranded. The mechanic on the phone says it sounds like the cluth needs replacing. How can you tell if it's the clutch and not the catalytic converter?