The big 3 beeing, exhaust system from catalytic to rear end on 3 inches, CAI witch is already done, SC.
After can consider gears and headers depending on issue that i look for.
Do the 3 inch fit the catalytic or Y pipe?
You guy's are really enthousiast, and let's say patient. But be aware i'm learning here. Lot's of proofing gonna go on.

 

If I recall (dont take my word on it because its been a while since ive had stock pipes), but i think the stock manifolds exited at 2.5" and stayed 2.5" through the cats into the y-pipe where it exited 3". It was 3" to the muffler.

What I'm currently running: Lontube headers (Pacesetter) with 3" collectors into a 3" pacesetter offroad Y-pipe (no more cats). The 3" continues into the SIDO magnaflow muffler where it exits in dual 2.5" into 4" stainless tips.

A cat back system is great to start with, but while you're in there welding, it would be very beneficial to put in an aftermarket y-pipe (magnaflow y is very popular). The stock y is EXTREMELY restrictive. They can be had for about $15.

 

As mentioned before, the big three, cat back, CAI and tuner. I feel none do a whole lot alone, but the combination starts working for you as you add mods that cmpliment the previos mods. After the big three, gears. If you are not going to the next step than shorty headers and Y pipe. If you are going to the next step than LT's, TC, and trans. Next level is heads and cam. Next stroker motor. It never really ends, but that is the fun of it. Set your goals, and plan carefully to reach it.
That's my 2 cents.... good luck

 

If I remember right, if torque is what your looking for out of some headers the Tri Y set up makes the most torque. I honestly don't know if anyone make them for our trucks but let me see what google says.

 

what the heck is a tri-y?

 

Instead of all four header tubes going into the collector at once 4>1, a TRI Y header looks like a Y because four into two and then into one pipe 4>2>1. I believe they were designed specifically for low end torque by improved scavenging effect. Here's a quick google image.

 

I wish I could fit a set of tri-Ys on my 07!

 

Apparently they have some for an '03
http://www.jegs.com/i/Doug+Thorley/702/199Y1/10002/-1

Other than that google's being a selfish C--T and not finding me any for other years

 

are those better than LTs? I've never even heard of a tri-y. And why would it only fit 03? Arent all the heads the same?

 

Now that's a little differnt....