easiest way is to remove mufler and run a bar through the cat to remove the insides. however keep in mind this is illegal in most states and on a 96 or newer it will fail inspection because your check engine light will come on. if the computer sees the same reading from the sensor behind the cat as the one in front of the cat, it sets a code saying that converter efficiancy is low. if the truck is quieter than it used to be the cat may be bad and need replacement.