I ran into this problem about a year ago. It was the Main Cat that wasn't clogged, but loose inside. The insulation that holds the ceramic honeycomb in place had disintegrated, thus causing the honeycomb to rattle around and tilt inside of the cat chamber. As a result...my car would barely go faster than 70!!! I bought a SHO y-pipe with cat and replaced the entire thing. This sounds more likely than the pre-cats being clogged.
Look around on the classifieds....you can find a used SHO y-pipe for around $200 and it's very easy to install. Heck...while you're at it...you might as well gut the pre-cats too! After you do the y-pipe and pre-cats....you'll marvel at how fast your 'tour is now.....I promise!
