ok, my CEL is on with the P0420 code...i have an 02 ex 5 spd coupe...my friend said that in order to change my cat, i would need to replace my header too? is this true? im in college kinda broke...what will i have to do to fix problem? o one more thing, whenever i get up to just past 4k rpm, my car lags really hard...any help would be appreciated...