First let me say this -->
Ok, now let me say that I know this probably needs to go under the exhuast forum.

Here is the system and it's so simple for the '03 4.2L

-JBA shorty headers $370
-High flow cats <-- still looking for good price
-Force II Flowmaster Exhaust $330

Horsepower stock -- 202 hp
Horsepower after upgrade (without cats) -- 225 to 230 hp

How do I know?
No, I haven't yet done this to my truck, but my friend did it to his and ran it on a dyno in my town. That was proof enough for me. I gotta admit, the power difference is amazing when you add a set of headers to your exhaust ... wow

 

Wow $1000.00 for a hole 25hp?? Doesn't sound like a very good deal to me.
Jimmy