2004 is the 5.7L, 346 C.I.D. LS1 “rated” at 350hp and 365lbs-ft of torque. 2005 and 2006 come with the 6.0L, 364 C.I.D. LS2 “rated” at 400hp/400lbs-ft of torque. Don’t get hung up thinking the LS2 is automatically a better vehicle because it has an extra 50hp and 35lbs-ft of torque from the factory. Both these engines are identical. The only way the LS2 makes it’* additional displacement is due to the increased bore. The block is the same, crank is the same, heck the heads and intake plenum are the same. Both motors respond identically to the same mods as LSx motors like to do. You can make a stout LS1 motor (like me) for cheap.
There are other minor differences between the 04’* and ‘05+ (other than cosmetic) in that ‘04’* have cable throttle, ‘05+ have ETC. The exhaust system was changed to accommodate the split duals in back vs. the 2 on the left like the ’04. But either one are still a true dual setup. Many think the stock ‘04’* sound better though! Brakes are improved on ‘05+ and of course the 18” wheels became an option. But both braking systems on either car are made by PBR. The handling and braking of the ’04, while not up to the standards of my Z28 prior, fail to disappoint me, and for the normal driver, the improvements on the ‘05+ won’t be readily apparent unless you take the car auto-x’ing every weekend! I had a blast with mine last Sunday on some nice high speed sweeping curves out mid-state. The tires finally started protesting causing me to back off some, when I attempted one sweeper at triple digit speeds. I had to scrub some MPH off to about 90 instead. Golly gee that’* terrible!!!
The PCM was also revised and is C.A.N. compliant for ‘05+.
If you remove these things from either car and look at the car from underneath, they are the same exact car!!
‘04’* are plagued with “cluster freak out” on “cooler” days. The cluster literally goes berserk on you out of nowhere for 10 seconds or so, then goes right back to normal as if nothing happened. It is a short to ground in the harness as well as a glitch in the IP board in the cluster that causes this. ‘05+ don’t have this issue, BUT, they have an issue with the ETC, where the pedal sensor shorts out, putting the car in “safe mode”. The LS2 in ‘05+ also has people complaining of excessive oil consumption. I don’t quite understand it because there isn’t an internal combustion engine on the planet that doesn’t consume oil, but I digress.
Then there is strut rub on ’04 & ’05 cars that people complain about. It seems that ‘06’* don’t have this issue. It only affects the 17” wheeled vehicles. Mine doesn’t suffer from this and mine was one of the first 465 ever built and shipped to the U.*., but there are many on our board that swear up, down, left, and right at GM over it.
So really, buy what fits your budget and needs best. Don’t discount an ’04 simply because it has the “dreaded” LS1 instead of the LS2. They’re both LSx motors and like above, are identical except for the bore. If you REALLY want hood scoops, you CAN get an ’05 hood put on an ’04 also!!