yeah it will, thats where the o2 simulator comes in to place

 

Ascertain a cat from the junk yard, gut it with a broom handle and then replace the existing one on your truck.

 

i gutted the cat in my 98 5.9 over a year ago and never pulled a check engine light, maybe im just lucky.

 

If you took out one "section" of honeycomb from that pic of the opened up cat, and slide the other half right in the middle, that's essentially a high flow cat. Also, the honeycomb "holes" are usually larger and let the exhaust gasses flow thru much easier.