I read somewhere in this forum or the TDR that the upgrade in the exhaust didn't much for improved HP... . and I'm sure that someone will correct me if I'm wrong..... I was under the impression that the 04. 5 had a 4" exhaust... .
If you talking about removing the cat... . I'd think again... in my home state it must be on the vehicle and must function when the vehicle goes through the emission test every 2 years.....
Today in my home state they can plug into OBDII port under the dash and tell if the cat is functioning... . without looking under the vehicle..... since its a high dollar item I would personally wouldn't be playing with it..... also if they find you've removed it and have run the vehicle they can fine you... ...
There are several ways to remove it..... remove its contents and put it back on the truck..... and take your chances.....
There are several advertisers on this web sight who have performance improvments for our trucks... . on the home page in the left column there is a link to the various advertisers... .
Hope this has been some help.....
Jim