I have a 97 lsc and for some time I lost some power and there is a rattle on the exaust so I think is the cat converter so I plan to eliminate all three cats would this be a good idea?

97 black on black LSC

Not unless you are sure that you don't have to have them for emissions reasons. And I'm pretty sure that you have upstream and downstream O2 sensors so that is going to play hell with your computer. It might even throw it into limp mode. That's why they make cat eliminator plug ins. They trick the computer to thinking that the downstream sensor readout is fine.

thanks for the info any idea where can I get teh plug ins?

97 black on black LSC

The O2 sensors after the converters just check the performance of the equipment before them.No limp mode- All that will happen if you remove all 3 converters is youll get a check engine light, youll have no adverse performance effects. You will most likely gain a tad bit of better upper rpm power, better exhaust note, and possibly better gas mileage. There are cheap ways of turning that check engine light off if you go through with removing the cats, do a google search with the words " spark plug anti foul o2 simulator". Ive used this setup in the past and it was cheap(less than 5.00) and effective at keeping the dash light away. All it basically does is move the tip of the post cat oxygen sensor out of the direct stream of exhaust gases so in essence the sensor thinks the gas has slowed down or the converters are still there...good luck