Definitely more to consider in CA. Just a little more info with a bit of searching.
It looks like a 2001 truck qualifies for catalytic converter replacement based on this site. Apparently, the converters have to be labeled to be legal.
http://www.californialegalconverters.com/store/Converters-California/What-Is-Legal K&N has a page that helps people determine if their kits are legal or not.
http://www.knfilters.com/streetlegal.htm My "guess" is that also an option would be to keep the airbox and change only the air filter.
Several tuners are 50 state legal. It means they can't turn any emission products off.