I used to have a '00 Silverado that was my daily driver. I'd done a good bit of work to it to make it a respectable performer. I used a pair of Casper's Electronics O2 simulators on it to eliminate the cats. They worked great, but are no longer available. I used them before I had a custom tune done on the computer. With EFI Live or HP Tuners, you can basically turn the O2 sensors off...no need for a simulator.