Does anyone know if there is a high flow y-pipe setup for a 2000 silverado with the 5.3 ext. cab short bed.

 

New stock converters flow great (at least on the trucks and C5's). Most people just leave them in place. They are not like the old crap ones from "back in the day".

If you need the few extra horsepower and want to stay legal, go with a set of Random Tech race cats. They are very expensive but flow great, but not much better than you think for the money.