I bought an aftermarket cat conv and it seems to be worse than the old (stock one). New/aftermarket is less than $125. New Toyota is above $700. Obviously the aftermarket one is a piece of junk. People have suggested running seafoam through the old cat to "renew" it. Is this the normal engine cleaner Seafoam (they other Seafoam for auto/marine and automatic trans). Which one do I buy? And by "running it through" the cat, do they mean taking it off and spraying this stuff through it (upright and in a bucket I would assume)?
Help, please.

1993 4Runner SR-5 4WD V-6 Auto Trans
1990 Pick-up (Hilux) 2WD SR-5 V-6 Auto Trans