How do you tell one year from the other.
 

And why is one year better than the other, Or are thay about the same? I saw a high school kid in one last week it was a auto he was runing it hard, A red one sounded great.

in 04 they had a 5.7 and no scoops on the hood

Only single outlet exhaust on the 04s as well. Interior is pretty much the same.

2004: Exhaust exits on left side rear only, 5.7 LS1, no hood scoops, cable throttle body
2005/2006: Split dual exhaust, 6.0 LS2, hood scoops (unless ordered without), drive by wire TB, bigger brakes, beefier (relatively) driveline
2006: Blacked out tail lights, lit steering wheel controls, door lock button on console

Of course, mixing and matching parts between years is popular. Lots of people put to 2006 tail lights on other years. '05/'06 scooped hoods are popular to put on '04s. I put the '06 lit steering wheel controls in my '05. There's a kit out there to add the console door lock button to '04/'05.

There are colors specific to various years too. The Brazen Orange Metallic was 2006, Barbados Blue Metallic was 2004 only. Yellow Jacket was 2004/2005. Spice Red was 2006 only. A few colors were available all three years.

You can pick up on most of these things here: http://www.ls1gto.com/forums/faq.php?

04 you could get the SAP(Sport Appearance Package) which had a hood with scoops, the new grills, and a ricer type rear spoiler-actually for cheaper than the 05 hood by itself! So it could still be an 04 with scoops.
Tailpipes are the easiest tip off.

I added the lock kit on my 04 as well as the SAP hood, sold the rear wing, still have the grilles in a box.

The SAP parts never included any kind of hood. The 2004s had a flat hood, the 2005/2006 models had a scooped hood but in 2005 you could option to a flat hood (only about 2 dozen 2005s were sold this way). Owners of 2004s could buy a new hood and have it retrofitted onto their car once the scooped hoods came out in 2005, but this was never considered part of the SAP parts group.

The various SAP parts were available starting in 2005 and could be purchased and installed at a dealership for any GTO already owned or new ones that came in.

The SAP parts that were available include:

-deeper recessed grills
-unique front lower valance (which was just glued and screwed to the existing bumper)
-unique rocker panels with "vents" (which replaced the existing stock rockers)
-unique rear bumper cover (which replaced the existing stock bumper) which required the used of the SAP exhaust which consisted of Magnaflow mufflers with dual tips on each side
-unique tall rear spoiler (which replaced the existing stock spoiler)

You are incorrect the " 2004 SAP Kit" did have the hood-I bought it at the dealer-specific part number for it, and as I said it was actually cheaper than the hood by itself from the dealer. I bought this car new off the showroom floor after the 05s had been out so maybe it was an SAP package for the 04 at that time. I sold the rear spoiler and still have the grilles that came in the package also.

From a dealer on the LS1GTO forums
"2004 Sports Appearance Package Available

--------------------------------------------------------------------------------

I Posted A Thread In Appearance Group. Gm Just Announced A Very Limited Release Appearance Package For 2004 Gto's. It Will Include
A 2005 Look A Like Hood For The 2004 (gm Tells Us The Hoods Are Not Interchangeable), Front Grille Insert And A Fancier Rear Spoiler. They Are Not Painted. Cannot Get Parts Separately. They Were Primarily Made For 2004 Gto's In Dealer Stock. In Fact, Dealers Cannot Even Order The Kits Thru Gm. They Are Being Distributed Thru Gm's "adi" Distributors (regional Gm Accessary Distributors). If You Want More Info Go To Appearance And Look For My Thread. If You Want Me To Order You One, You Can Email Me. We Are In California. Will Sell Them For $1400 Plus Shipping Costs.
Your Local Dealer Can Get Them As Well. Thy May Not Know About It. Have Them Go To Gm Messenger Board And The Messange Number Is Acc05-001
Dms "

The 05-06 SAP had all the valence/bumper stuff and since the exhaust was different would not fit.

I stand corrected. I did a bit of digging and found information about what Pontiac first called the retro package and later renamed it the 2004 SAP. Not to be confused with the 05/06 SAP which was different.

I never knew a 2004 package existed. Thanks for the clarification, glad to learn something new. All I knew about previously was the 05/06 SAP.

I was really glad when I got it it was cheaper than the hood by itself-had to have scoops on a GTO of any year right!