Your precats are likely falling apart & clogging the main cat. The purpose of the pre-cats is to scrub exhaust emssions for the few minutes when the engine is cold. After that, your main cat does the job just fine by itself. Many opt to 'gut' their pre-cats rather than spend huge amounts of money to replace them. New precats are a dealer only item & very expensive - on the order of $1500 installed, usually more.
ALTERNATIVE 1:
If you're not comfortable turning a wrench, you can pick up a set of "mytery modded" pre-cats from buckshotmotorsports.com for $80 after core charges, and replace yours - labor cost $200 - $300. Once done, have a new high-flow cat installed at a local muffler shop - $80 parts, $50 labor.
ALTERNATIVE 2:
Call on the happy CEGers in your area to come & mystery mod your pre-cats for you. Some will do the job for the cost of a case of beer. Then all you'll have left to do is visit that muffler shop & have the main cat replaced.
Jim R
